File System Tuning Guide File System Tuning Guide
StorNext® 3.1.4.1
6-01376-15 Rev A
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Contents
Distributed LAN Servers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
Distributed LAN Client Vs. Legacy Network Attached Storage . . . . . . . 23
Windows Memory Requirements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
Sample FSM Configuration File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
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Contents
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StorNext File System Tuning
The StorNext File System (SNFS) provides extremely high performance
for widely varying scenarios. Many factors determine the level of
performance you will realize. In particular, the performance
characteristics of the underlying storage system are the most critical
factors. However, other components such as the Metadata Network and
MDC systems also have a significant effect on performance.
Furthermore, file size mix and application I/O characteristics may also
present specific performance requirements, so SNFS provides a wide
variety of tunable settings to achieve optimal performance. It is usually
best to use the default SNFS settings, because these are designed to
provide optimal performance under most scenarios. However, this guide
discusses circumstances in which special settings may offer a
performance benefit.
The Underlying Storage System
The performance characteristics of the underlying storage system are
the most critical factors for file system performance. Typically, RAID
storage systems provide many tuning options for cache settings, RAID
level, segment size, stripe size, and so on.
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The Underlying Storage System
RAID Cache
Configuration
The single most important RAID tuning component is the cache
configuration. This is particularly true for small I/O operations.
Contemporary RAID systems such as the EMC CX series and the various
Engenio systems provide excellent small I/O performance with properly
tuned caching. So, for the best general purpose performance
characteristics, it is crucial to utilize the RAID system caching as fully as
possible.
For example, write-back caching is absolutely essential for metadata
stripe groups to achieve high metadata operations throughput.
However, there are a few drawbacks to consider as well. For example,
read-ahead caching improves sequential read performance but might
reduce random performance. Write-back caching is critical for small
write performance but may limit peak large I/O throughput.
Caution: Some RAID systems cannot safely support write-back
caching without risk of data loss, which is not suitable for
critical data such as file system metadata.
Consequently, this is an area that requires an understanding of
application I/O requirements. As a general rule, RAID system caching is
critically important for most applications, so it is the first place to focus
tuning attention.
RAID Write-Back
Caching
Write-back caching dramatically reduces latency in small write
operations. This is accomplished by returning a successful reply as soon
as data is written into cache, and then deferring the operation of
actually writing the data to the physical disks. This results in a great
performance improvement for small I/O operations.
Many contemporary RAID systems protect against write-back cache data
loss due to power or component failure. This is accomplished through
various techniques including redundancy, battery backup, battery-
backed memory, and controller mirroring. To prevent data corruption, it
is important to ensure that these systems are working properly. It is
particularly catastrophic if file system metadata is corrupted, because
complete file system loss could result. Check with your RAID vendor to
make sure that write-back caching is safe to use.
Minimal I/O latency is critically important for metadata stripe groups to
achieve high metadata operations throughput. This is because metadata
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operations involve a very high rate of small writes to the metadata disk,
so disk latency is the critical performance factor. Write-back caching can
be an effective approach to minimizing I/O latency and optimizing
metadata operations throughput. This is easily observed in the hourly
File System Manager (FSM) statistics reports in the cvlog file. For
example, here is a message line from the cvlog file:
PIO HiPriWr SUMMARY SnmsMetaDisk0 sysavg/350 sysmin/333 sysmax/
367
This statistics message reports average, minimum, and maximum write
latency (in microseconds) for the reporting period. If the observed
average latency exceeds 500 microseconds, peak metadata operation
throughput will be degraded. For example, create operations may be
around 2000 per second when metadata disk latency is below 500
microseconds. However, if metadata disk latency is around 5
milliseconds, create operations per second may be degraded to 200 or
worse.
Another typical write caching approach is a “write-through.” This
approach involves synchronous writes to the physical disk before
returning a successful reply for the I/O operation. The write-through
approach exhibits much worse latency than write-back caching;
therefore, small I/O performance (such as metadata operations) is
severely impacted. It is important to determine which write caching
approach is employed, because the performance observed will differ
greatly for small write I/O operations.
In some cases, large write I/O operations can also benefit from caching.
However, some SNFS customers observe maximum large I/O throughput
by disabling caching. While this may be beneficial for special large I/O
scenarios, it severely degrades small I/O performance; therefore, it is
suboptimal for general-purpose file system performance.
RAID Read-Ahead
Caching
RAID read-ahead caching is a very effective way to improve sequential
read performance for both small (buffered) and large (DMA) I/O
operations. When this setting is utilized, the RAID controller pre-fetches
disk blocks for sequential read operations. Therefore, subsequent
application read operations benefit from cache speed throughput,
which is faster than the physical disk throughput.
This is particularly important for concurrent file streams and mixed I/O
streams, because read-ahead significantly reduces disk head movement
that otherwise severely impacts performance.
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The Underlying Storage System
While read-ahead caching improves sequential read performance, it
does not help highly transactional performance. Furthermore, some
SNFS customers actually observe maximum large sequential read
throughput by disabling caching. While disabling read-ahead is
beneficial in these unusual cases, it severely degrades typical scenarios.
Therefore, it is unsuitable for most environments.
RAID Level, Segment
Size, and Stripe Size
Configuration settings such as RAID level, segment size, and stripe size
are very important and cannot be changed after put into production, so
it is critical to determine appropriate settings during initial
configuration.
The best RAID level to use for high I/O throughput is usually RAID5. The
stripe size is determined by the product of the number of disks in the
RAID group and the segment size. For example, a 4+1 RAID5 group
with 64K segment size results in a 256K stripe size. The stripe size is a
very critical factor for write performance because I/Os smaller than the
stripe size may incur a read/modify/write penalty. It is best to configure
RAID5 settings with no more than 512K stripe size to avoid the read/
modify/write penalty. The read/modify/write penalty is most noticeable
in the absence of “write-back” caching being performed by the RAID
controller.
The RAID stripe size configuration should typically match the SNFS
StripeBreadth configuration setting when multiple LUNs are utilized in a
stripe group. However, in some cases it might be optimal to configure
the SNFS StripeBreadth as a multiple of the RAID stripe size, such as
when the RAID stripe size is small but the user's I/O sizes are very large.
However, this will be suboptimal for small I/O performance, so may not
be suitable for general purpose usage.
RAID1 mirroring is the best RAID level for metadata and journal storage
because it is most optimal for very small I/O sizes. Quantum
recommends using fibre channel or SAS disks (as opposed to SATA) for
metadata and journal due to the higher IOPS performance and
reliability. It is also very important to allocate entire physical disks for
the Metadata and Journal LUNs in ordep to avoid bandwidth contention
with other I/O traffic. Metadata and Journal storage requires very high
IOPS rates (low latency) for optimal performance, so contention can
severely impact IOPS (and latency) and thus overall performance. If
Journal I/O exceeds 1ms average latency, you will observe significant
performance degradation.
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File Size Mix and Application I/O Characteristics
It can be useful to use a tool such as lmdd to help determine the storage
system performance characteristics and choose optimal settings. For
example, varying the stripe size and running lmdd with a range of I/O
sizes might be useful to determine an optimal stripe size multiple to
configure the SNFS StripeBreadth.
Some storage vendors now provide RAID6 capability for improved
reliability over RAID5. This may be particularly valuable for SATA disks
where bit error rates can lead to disk problems. However, RAID6
typically incurs a performance penalty compared to RAID5, particularly
for writes. Check with your storage vendor for RAID5 versus RAID6
recommendations.
File Size Mix and Application I/O Characteristics
It is always valuable to understand the file size mix of the target dataset
as well as the application I/O characteristics. This includes the number of
concurrent streams, proportion of read versus write streams, I/O size,
sequential versus random, Network File System (NFS) or Common
Internet File System (CIFS) access, and so on.
For example, if the dataset is dominated by small or large files, various
settings can be optimized for the target size range.
Similarly, it might be beneficial to optimize for particular application I/O
characteristics. For example, to optimize for sequential 1MB I/O size it
would be beneficial to configure a stripe group with four 4+1 RAID5
LUNs with 256K stripe size.
However, optimizing for random I/O performance can incur a
performance trade-off with sequential I/O.
Furthermore, NFS and CIFS access have special requirements to consider
as described in the Direct Memory Access (DMA) I/O Transfer section.
Direct Memory Access
(DMA) I/O Transfer
To achieve the highest possible large sequential I/O transfer throughput,
SNFS provides DMA-based I/O. To utilize DMA I/O, the application must
issue its reads and writes of sufficient size and alignment. This is called
well-formed I/O. See the mount command settings auto_dma_read_length
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File Size Mix and Application I/O Characteristics
and auto_dma_write_length, described in the Mount Command Options
on page 19.
Buffer Cache
Reads and writes that aren't well-formed utilize the SNFS buffer cache.
This also includes NFS or CIFS-based traffic because the NFS and CIFS
daemons defeat well-formed I/Os issued by the application.
There are several configuration parameters that affect buffer cache
performance. The most critical is the RAID cache configuration because
buffered I/O is usually smaller than the RAID stripe size, and therefore
incurs a read/modify/write penalty. It might also be possible to match
the RAID stripe size to the buffer cache I/O size. However, it is typically
described earlier in this document.
It is usually best to configure the RAID stripe size no greater than 256K
for optimal small file buffer cache performance.
For more buffer cache configuration settings, see Mount Command
Options on page 19.
NFS / CIFS
It is best to isolate NFS and/or CIFS traffic off of the metadata network
to eliminate contention that will impact performance. For optimal
performance it is necessary to use 1000BaseT instead of 100BaseT. On
NFS clients, use the vers=3, rsize=262144 and wsize=262144 mount
options, and use TCP mounts instead of UDP. When possible, it is also
best to utilize TCP Offload capabilities as well as jumbo frames.
It is best practice to have clients directly attached to the same network
switch as the NFS or CIFS server. Any routing required for NFS or CIFS
traffic incurs additional latency that impacts performance.
It is critical to make sure the speed/duplex settings are correct, because
this severely impacts performance. Most of the time auto-detect is the
correct setting. Some managed switches allow setting speed/duplex (for
example 1000Mb/full,) which disables auto-detect and requires the host to
be set exactly the same. However, if the settings do not match between
switch and host, it severely impacts performance. For example, if the
switch is set to auto-detect but the host is set to 1000Mb/full, you will
observe a high error rate along with extremely poor performance. On
Linux, the ethtool tool can be very useful to investigate and adjust speed/
duplex settings.
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SNFS and Virus Checking
If performance requirements cannot be achieved with NFS or CIFS,
consider using a StorNext Distributed LAN client or fibre-channel
attached client.
It can be useful to use a tool such as netperf to help verify network
performance characteristics.
SNFS and Virus Checking
Virus-checking software can severely degrade the performance of any
file system, including SNFS. If you have anti-virus software running on a
Windows Server 2003 or Windows XP machine, Quantum recommends
configuring the software so that it does NOT check SNFS.
The Metadata Network
As with any client/server protocol, SNFS performance is subject to the
limitations of the underlying network. Therefore, it is recommended
that you use a dedicated Metadata Network to avoid contention with
other network traffic. Either 100BaseT or 1000BaseT is required, but for
a dedicated Metadata Network there is usually no benefit from using
1000BaseT over 100BaseT. Neither TCP offload nor are jumbo frames
required.
It is best practice to have all SNFS clients directly attached to the same
network switch as the MDC systems. Any routing required for metadata
traffic will incur additional latency that impacts performance.
It is critical to ensure that speed/duplex settings are correct, as this will
severely impact performance. Most of the time auto-detect is the correct
setting. Some managed switches allow setting speed/duplex, such as
100Mb/full, which disables auto-detect and requires the host to be set
exactly the same. However, performance is severely impacted if the
settings do not match between switch and host. For example, if the
switch is set to auto-detect but the host is set to 100Mb/full, you will
observe a high error rate and extremely poor performance. On Linux the
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ethtool tool can be very useful to investigate and adjust speed/duplex
settings.
It can be useful to use a tool like netperf to help verify the Metadata
Network performance characteristics. For example, if netperf -t TCP_RR
reports less than 15,000 transactions per second capacity, a
performance penalty may be incurred. You can also use the netstat tool
to identify tcp retransmissions impacting performance. The cvadmin
“latency-test” tool is also useful for measuring network latency.
Note the following configuration requirements for the metadata
network:
• In cases where gigabit networking hardware is used and maximum
StorNext performance is required, a separate, dedicated switched
Ethernet LAN is recommended for the StorNext metadata network.
If maximum StorNext performance is not required, shared gigabit
networking is acceptable.
• A separate, dedicated switched Ethernet LAN is mandatory for the
metadata network if 100 Mbit/s or slower networking hardware is
used.
• StorNext does not support file system metadata on the same
network as iSCSI, NFS, CIFS, or VLAN data when 100 Mbit/s or
slower networking hardware is used.
The Metadata Controller System
The CPU power and memory capacity of the MDC System are important
performance factors, as well as the number of file systems hosted per
system. In order to ensure fast response time it is necessary to use
dedicated systems, limit the number of file systems hosted per system
(maximum 8), and have an adequate CPU and memory.
Some metadata operations such as file creation can be CPU intensive,
and benefit from increased CPU power. The MDC platform is important
in these scenarios because lower clock- speed CPUs such as Sparc
degrade performance.
Other operations can benefit greatly from increased memory, such as
directory traversal. SNFS provides three config file settings that can be
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used to realize performance gains from increased memory:
BufferCacheSize, InodeCacheSize, and ThreadPoolSize.
However, it is critical that the MDC system have enough physical
memory available to ensure that the FSM process doesn’t get swapped
out. Otherwise, severe performance degradation and system instability
can result.
The operating system on the metadata controller must always be run in
U.S. English.
FSM Configuration File
Settings
The following FSM configuration file settings are explained in greater
detail in the cvfs_config man page. For a sample FSM configuration file,
see Sample FSM Configuration File on page 27.
The examples in the following sections are excerpted from the sample
configuration file from Sample FSM Configuration File on page 27.
Stripe Groups
Splitting apart data, metadata, and journal into separate stripe groups
is usually the most important performance tactic. The create, remove,
and allocate (e.g., write) operations are very sensitive to I/O latency of
the journal stripe group. Configuring a separate stripe group for journal
greatly benefits the speed of these operations because disk seek latency
is minimized. However, if create, remove, and allocate performance
aren't critical, it is okay to share a stripe group for both metadata and
journal, but be sure to set the exclusive property on the stripe group so
it doesn't get allocated for data as well. It is recommended that you
assign only a single LUN for each journal or metadata stripe group.
Multiple metadata stripe groups can be utilized to increase metadata I/
O throughput through concurrency. RAID1 mirroring is optimal for
metadata and journal storage. Utilizing the write-back caching feature
of the RAID system (as described previously) is critical to optimizing
performance of the journal and metadata stripe groups.
Example:
[stripeGroup RegularFiles]
Status UP
Exclusive No
for all Files##
Read Enabled
Write Enabled
##Non-Exclusive stripeGroup
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StripeBreadth 256K
MultiPathMethod Rotate
Node CvfsDisk6 0
Node CvfsDisk7 1
[StripeGroup MetaFiles]
Status UP
MetaData Yes
Journal No
Exclusive Yes
Read Enabled
Write Enabled
StripeBreadth 256K
MultiPathMethod Rotate
Node CvfsDisk0 0
[StripeGroup JournFiles]
Status UP
Journal Yes
MetaData No
Exclusive Yes
Read Enabled
Write Enabled
StripeBreadth 256K
MultiPathMethod Rotate
Node CvfsDisk1 0
Affinities
Affinities are another stripe group feature that can be very beneficial.
Affinities can direct file allocation to appropriate stripe groups
according to performance requirements. For example, stripe groups can
be set up with unique hardware characteristics such as fast disk versus
slow disk, or wide stripe versus narrow stripe. Affinities can then be
employed to steer files to the appropriate stripe group.
For optimal performance, files that are accessed using large DMA-based
I/O could be steered to wide-stripe stripe groups. Less performance-
critical files could be steered to slow disk stripe groups. Small files could
be steered to narrow-stripe stripe groups.
Example:
[stripeGroup AudioFiles]
Status UP
Exclusive Yes
stripeGroup ##
##These two lines set Exclusive
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Affinity AudFiles
Read Enabled
##for Audio Files Only##
Write Enabled
StripeBreadth 1M
MultiPathMethod Rotate
Node CvfsDisk4 0
Node CvfsDisk5 1
Note: Affinity names cannot be longer than eight characters.
StripeBreadth
This setting must match the RAID stripe size or be a multiple of the RAID
stripe size. Matching the RAID stripe size is usually the most optimal
setting. However, depending on the RAID performance characteristics
and application I/O size, it might be beneficial to use a multiple of the
RAID stripe size. For example, if the RAID stripe size is 256K, the stripe
group contains 4 LUNs, and the application to be optimized uses DMA I/
O with 8MB block size, a StripeBreadth setting of 2MB might be optimal.
In this example the 8MB application I/O is issued as 4 concurrent 2MB I/
Os to the RAID. This concurrency can provide up to a 4X performance
increase. This typically requires some experimentation to determine the
RAID characteristics. The lmdd utility can be very helpful. Note that this
setting is not adjustable after initial file system creation.
Optimal range for the StripeBreadth setting is 128K to multiple
megabytes, but this varies widely. This setting cannot be changed after
being put into production, so its important to choose the setting
carfefully during initial configuration.
Example:
[stripeGroup VideoFiles]
Status UP
Exclusive Yes
##These Two lines set Exclusive
stripeGroup##
Affinity VidFiles
Read Enabled
##for Video Files Only##
Write Enabled
StripeBreadth 4M
MultiPathMethod Rotate
Node CvfsDisk2 0
Node CvfsDisk3 1
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BufferCacheSize
This setting consumes up to 2X bytes of memory times the number
specified. Increasing this value can reduce latency of any metadata
operation by performing a hot cache access to directory blocks, inode
information, and other metadata info. This is about 10 to 1000 times
faster than I/O. It is especially important to increase this setting if
metadata I/O latency is high, (for example, more than 2ms average
latency). We recommend sizing this according to how much memory is
available; more is better. Optimal settings for BufferCacheSize range
from 16MB to 128MB.
Example: # BufferCacheSize 64M
# default 32MB
InodeCacheSize
This setting consumes about 800-1000 bytes of memory times the
number specified. Increasing this value can reduce latency of any
metadata operation by performing a hot cache access to inode
information instead of an I/O to get inode info from disk, about 100 to
1000 times faster. It is especially important to increase this setting if
metadata I/O latency is high, (for example, more than 2ms average
latency). You should try to size this according to the sum number of
working set files for all clients. Optimal settings for InodeCacheSize
range from 16K to 128K.
Example: InodeCacheSize 16K # 1000-1200 bytes each, default
8K
ThreadPoolSize
This setting consumes up to 512 KB memory times the number
specified. Increasing this value can improve concurrency of metadata
operations. For example, if many client processes are executing
concurrently, the thread pool can become exhausted by I/O wait time.
Increasing the thread pool size permits hot cache operations to be
processed that would otherwise be backed up behind the I/O-bound
operations. There are various O/S limits to the number of threads that
can cause fatal problems for the FSM daemon, so it's not a good idea to
set this setting too high. A range from 32 to 128 is recommended,
depending on the amount of available memory. It is recommended to
size it according to the max threads FSM hourly statistic reported in the
cvlog file. Optimal settings for ThreadPoolSize range from 32K to 128K.
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Example: ThreadPoolSize 32
thread
# default 16, 512 KB memory per
ForcestripeAlignment
This setting should always be set to Yes. This is critical if the largest
StripeBreadth defined is greater than 1MB. Note that this setting is not
adjustable after initial file system creation.
Example: ForcestripeAlignment
Yes
FsBlockSize
The FsBlockSize (FSB), metadata disk size, and JournalSize settings all
work together. For example, the FsBlockSize must be set correctly in
order for the metadata sizing to be correct. JournalSize is also
dependent on the FsBlockSize.
For FsBlockSize the optimal settings for both performance and space
utilization are in the range of 16K or 64K.Settings greater than 64K are
not recommended because performance will be adversely impacted due
to inefficient metadata I/O operations. Values less than 16K are not
recommended in most scenarios because startup and failover time may
be adversely impacted. Setting FsBlockSize to higher values is
important for multiterabyte file systems for optimal startup and failover
time.
Note: This is particularly true for slow CPU clock speed metadata
servers such as Sparc. However, values greater than 16K can
severely consume metadata space in cases where the file-to-
directory ratio is low (e.g. less than 100 to 1).
For metadata disk size, you must have a minimum of 25 GB, with more
space allocated depending on the number of files per directory and the
size of your file system.
The following table shows suggested FsBlockSize (FSB) settings and
metadata disk space based on the average number of files per directory
and file system size. The amount of disk space listed for metadata is in
addition to the 25 GB minimum amount. Use this table to determine the
setting for your configuration.
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Average No.
of Files Per
Directory
File System SIze: Less
Than 10TB
File System Size: 10TB
or Larger
Less than 10
FSB: 16KB
FSB: 64KB
Metadata: 32 GB per 1M Metadata: 128 GB per
files
1M files
10-100
FSB: 16KB
FSB: 64KB
Metadata: 8 GB per 1M
files
Metadata: 32 GB per 1M
files
100-1000
1000 +
FSB: 64KB
FSB: 64KB
Metadata: 8 GB per 1M
files
Metadata: 8 GB per 1M
files
FSB: 64KB
FSB: 64KB
Metadata: 4 GB per 1M
files
Metadata: 4 GB per 1M
files
This setting is not adjustable after initial file system creation, so it is very
important to give it careful consideration during initial configuration.
Example: FsBlockSize
16K
JournalSize
The optimal settings for JournalSize are in the range between 16M and
64M, depending on the FsBlockSize. Avoid values greater than 64M
due to potentially severe impacts on startup and failover times. Values
at the higher end of the 16M-64M range may improve performance of
metadata operations in some cases, although at the cost of slower
startup and failover time.
The following table shows recommended settings. Choose the setting
that corresponds to your configuration.
FsBlockSize
JournalSize
16KB
64KB
16MB
64MB
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This setting is adjustable using the cvupdatefs utility. For more
information, see the cvupdatefs man page.
Example: JournalSize 16M
SNFS Tools
The snfsdefrag tool is very useful to identify and correct file extent
fragmentation. Reducing extent fragmentation can be very beneficial
for performance. You can use this utility to determine whether files are
fragmented, and if so, fix them. If your files are prone to fragmentation
you should also use the FSM config file tuning options to minimize
fragmentation. These global configuration settings are InodeExpandMin,
InodeExpandInc, and InodeExpandMax. (For more information, see the
man cvfs_config page.) The snfsdefrag man page explains the command
options in greater detail.
FSM hourly statistics reporting is another very useful tool. This can show
you the mix of metadata operations being invoked by client processes,
as well as latency information for metadata operations and metadata
and journal I/O. This information is easily accessed in the cvlog log files.
All of the latency oriented stats are reported in microsecond units.
It also possible to trigger an instant FSM statistics report by setting the
Once Only debug flag using cvadmin. For example:
cvadmin -F snfs1 -e ‘debug 0x01000000’ ; tail -100 /usr/
cvfs/data/snfs1/log/cvlog
The following items are a few things to watch out for:
• A non-zero value for FSM wait SUMMARY journal waits indicates
insufficient IOPS performance of the disks assigned to the metadata
stripe group. This usually requires reducing the metadata I/O latency
time by adjusting RAID cache settings or reducing bandwidth
contention for the metadata LUN. Another possible solution is to
add another metadata stripe group to the file system. This will
improve metadata ops performance through I/O concurrency.
• Non-zero value for FSM wait SUMMARY free buffer waits or low hit
ratio for FSM cache SUMMARY buffer lookups indicates the FSM
configuration setting BufferCacheSize is insufficient.
• Non-zero value for FSM wait SUMMARY free inode waits or low hit
ratio for FSM cache SUMMARY inode lookups indicates the FSM
configuration setting InodeCacheSize is insufficient.
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• Large value for FSM threads SUMMARY max busy indicates the FSM
configuration setting ThreadPoolSize is insufficient.
• Extremely high values for FSM cache SUMMARY inode lookups, TKN
SUMMARY TokenRequestV3, or TKN SUMMARY TokenReqAlloc might
indicate excessive file fragmentation. If so, the snfsdefrag utility can
be used to fix the fragmented files.
• The VOP and TKN summary statistics of the form count avg/q+e
min/q+e max/q+e show microsecond queue and execution latency
for the various metadata operations. This shows what type of
metadata operations are most prevalent and most costly. These are
also broken out per client, which can be useful to identify a client
that is disproportionately loading the FSM.
SNFS supports the Windows Perfmon utility. This provides many useful
statistics counters for the SNFS client component. To install, obtain a
copy of cvfsperf.dll from the SCM team in Denver and copy it into the c:/
winnt/system32 directory on the SNFS client system. Then run
rmperfreg.exe and instperfreg.exe to set up the required registry settings.
After these steps, the SNFS counters should be visible to the Windows
Perfmon utility. If not, check the Windows Application Event log for
errors.
The cvcp utility is a higher performance alternative to commands such
as cp and tar. The cvcp utility achieves high performance by using
threads, large I/O buffers, preallocation, stripe alignment, DMA I/O
transfer, and Bulk Create. Also, the cvcp utility uses the SNFS External
API for preallocation and stripe alignment. In the directory-to-directory
copy mode (for example, cvcp source_dir destination_dir,) cvcp
conditionally uses the Bulk Create API to provide a dramatic small file
copy performance boost. However, it will not use Bulk Create in some
scenarios, such as non-root invocation, managed file systems, quotas,
or Windows security. Hopefully, these limitations will be removed in a
future release. When Bulk Create is utilized, it significantly boosts
performance by reducing the number of metadata operations issued.
For example, up to 20 files can be created all with a single metadata
operation. For more information, see the cvcp man page.
The cvmkfile utility provides a command line tool to utilize valuable
SNFS performance features. These features include preallocation, stripe
alignment, and affinities. See the cvmkfile man page.
The Lmdd utility is very useful to measure raw LUN performance as well
as varied I/O transfer sizes.
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The Metadata Controller System
The cvdbset utility has a special “Perf” trace flag that is very useful to
analyze I/O performance. For example: cvdbset perf
Then, you can use cvdb -g to collect trace information such as this:
PERF: Device Write 41 MB/s IOs 2 exts 1 offs 0x0 len 0x400000 mics
95589 ino 0x5
PERF: VFS Write EofDmaAlgn 41 MB/s offs 0x0 len 0x400000 mics 95618
ino 0x5
The “PERF: Device” trace shows throughput measured for the device I/O.
It also shows the number of I/Os into which it was broken, and the
number of extents (sequence of consecutive filesystem blocks).
The “PERF: VFS” trace shows throughput measured for the read or write
system call and significant aspects of the I/O, including:
• Dma: DMA
• Buf: Buffered
• Eof: File extended
• Algn: Well-formed DMA I/O
• Shr: File is shared by another client
• Rt: File is real time
• Zr: Hole in file was zeroed
Both traces also report file offset, I/O size, latency (mics), and inode
number.
Sample use cases:
• Verify that I/O properties are as expected.
You can use the VFS trace to ensure that the displayed properties
are consistent with expectations, such as being well formed;
buffered versus DMA; shared/non-shared; or I/O size. If a small I/O is
being performed DMA, performance will be poor. If DMA I/O is not
well formed, it requires an extra data copy and may even be broken
into small chunks. Zeroing holes in files has a performance impact.
• Determine if metadata operations are impacting performance.
If VFS throughput is inconsistent or significantly less than Device
throughput, it might be caused by metadata operations. In that
case, it would be useful to display “fsmtoken,” “fsmvnops,” and
“fsmdmig” traces in addition to “perf.”
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The Metadata Controller System
• Identify disk performance issues.
If Device throughput is inconsistent or less than expected, it might
indicate a slow disk in a stripe group, or that RAID tuning is
necessary.
• Identify file fragmentation.
If the extent count “exts” is high, it might indicate a fragmentation
problem.This causes the device I/Os to be broken into smaller
chunks, which can significantly impact throughput.
• Identify read/modify/write condition.
If buffered VFS writes are causing Device reads, it might be
beneficial to match I/O request size to a multiple of the
“cachebufsize” (default 64KB; see mount_cvfs man page). Another
way to avoid this is by truncating the file before writing.
The cvadmin command includes a latency-test utility for measuring the
latency between an FSM and one or more SNFS clients. This utility
causes small messages to be exchanged between the FSM and clients as
quickly as possible for a brief period of time, and reports the average
time it took for each message to receive a response.
The latency-test command has the following syntax:
latency-test index-number [seconds]
latency-test all [seconds]
If an index-number is specified, the test is run between the currently-
selected FSM and the specified client. (Client index numbers are
displayed by the cvadmin who command). If all is specified, the test is
run against each client in turn.
The test is run for 2 seconds, unless a value for seconds is specified.
Here is a sample run:
snadmin (lsi) > latency-test
Test started on client 1 (bigsky-node2)... latency 55us
Test started on client 2 (k4)... latency 163us
There is no rule-of-thumb for “good” or “bad” latency values. Latency
can be affected by CPU load or SNFS load on either system, by unrelated
Ethernet traffic, or other factors. However, for otherwise idle systems,
differences in latency between different systems can indicate differences
in hardware performance. (In the example above, the difference is a
Gigabit Ethernet and faster CPU versus a 100BaseT Ethernet and a
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The Metadata Controller System
slower CPU.) Differences in latency over time for the same system can
indicate new hardware problems, such as a network interface going
bad.
If a latency test has been run for a particular client, the cvadmin who
long command includes the test results in its output, along with
information about when the test was last run.
Mount Command
Options
The following SNFS mount command settings are explained in greater
detail in the mount_cvfs man page.
The default size of the buffer cache varies by platform and main
memory size, and ranges between 32MB and 256MB. And, by default,
each buffer is 64K so the cache contains between 512 and 4096 buffers.
In general, increasing the size of the buffer cache will not improve
performance for streaming reads and writes. However, a large cache
helps greatly in cases of multiple concurrent streams, and where files
are being written and subsequently read. Buffer cache size is adjusted
with the buffercachecap setting.
The buffer cache I/O size is adjusted using the cachebufsize setting. The
default setting is usually optimal; however, sometimes performance can
be improved by increasing this setting to match the RAID5 stripe size.
Using a large cachebufsize setting decreases random I/O performance
when the amount of data being read is smaller than the cache buffer
size.
Buffer cache read-ahead can be adjusted with the
buffercache_readahead setting. When the system detects that a file is
being read in its entirety, several buffer cache I/O daemons pre-fetch
data from the file in the background for improved performance. The
default setting is optimal in most scenarios.
The auto_dma_read_length and auto_dma_write_length settings
determine the minimum transfer size where direct DMA I/O is
performed instead of using the buffer cache for well-formed I/O. These
settings can be useful when performance degradation is observed for
small DMA I/O sizes compared to buffer cache.
For example, if buffer cache I/O throughput is 200 MB/sec but 512K
DMA I/O size observes only 100MB/sec, it would be useful to determine
which DMA I/O size matches the buffer cache performance and adjust
auto_dma_read_length and auto_dma_write_length accordingly. The lmdd
utility is handy here.
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The Distributed LAN (Disk Proxy) Networks
The dircachesize option sets the size of the directory information cache
on the client. This cache can dramatically improve the speed of readdir
operations by reducing metadata network message traffic between the
SNFS client and FSM. Increasing this value improves performance in
scenarios where very large directories are not observing the benefit of
the client directory cache.
SNFS External API
The SNFS External API might be useful in some scenarios because it
offers programmatic use of special SNFS performance capabilities such
as affinities, preallocation, and quality of service. For more information,
see the Quality of Service chapter of the StorNext User’s Guide API Guide.
The Distributed LAN (Disk Proxy) Networks
As with any client/server protocol, SNFS Distributed LAN performance is
subject to the limitations of the underlying network. Therefore, it is
strongly recommended that you use Gigabit (1000BaseT) for Distributed
LAN traffic. Neither TCP offload nor jumbo frames are required.
Hardware
Configuration
SNFS Distributed LAN can easily fill several Gigabit Ethernets with data,
so take special care when selecting and configuring the switches used to
interconnect SNFS Distributed LAN clients and servers. Ensure that your
network switches have enough internal bandwidth to handle all of the
anticipated traffic between all Distributed LAN clients and servers
connected to them.
A network switch that is dropping packets will cause TCP
retransmissions. This can be easily observed on both Linux and Windows
platforms by using the netstat -s command while Distributed LAN is in
progress. Reducing the TCP window size used by Distributed LAN might
also help with an oversubscribed network switch. The Windows client
Distributed LAN tab and the Linux dpserver file contain the tuning
parameter for the TCP window size. Note that Distributed LAN server
remounts are required after changing this parameter.
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The Distributed LAN (Disk Proxy) Networks
It is best practice to have all SNFS Distributed LAN clients and servers
directly attached to the same network switch. A router between a
Distributed LAN client and server could be easily overwhelmed by the
data rates required.
It is critical to ensure that speed/duplex settings are correct, as this will
severely impact performance. Most of the time auto-detect is the
correct setting. Some managed switches allow setting speed/duplex,
such as 1000Mb/full, which disables auto-detect and requires the host
to be set exactly the same. However, performance is severely impacted if
the settings do not match between switch and host. For example, if the
switch is set to auto-detect but the host is set to 1000Mb/full, you will
observe a high error rate and extremely poor performance. On Linux the
ethtool command can be very useful to investigate and adjust speed/
duplex settings.
In some cases, TCP offload seems to cause problems with Distributed
LAN by miscalculating checksums under heavy loads. This is indicated by
bad segments indicated in the output of netstat -s. On Linux, the TCP
offload state can be queried by running ethtool -k, and modified by
running ethtool -K. On Windows it is configured through the Advanced
tab of the configuration properties for a network interface.
The internal bus bandwidth of a Distributed LAN client or server can also
place a limit on performance. A basic PCI- or PCI-X-based workstation
might not have enough bus bandwidth to run multiple Gigabit Ethernet
NICs at full speed; PCI Express is recommended but not required.
Similarly, the performance characteristics of NICs can vary widely and
ultimately limit the performance of Distributed LAN. For example, some
NICs might be able to transmit or receive each packet at Gigabit speeds,
but not be able to sustain the maximum needed packet rate. An
inexpensive 32-bit NIC plugged into a 64-bit PCI-X slot is incapable of
fully utilizing the host's bus bandwidth.
It can be useful to use a tool like netperf to help verify the performance
characteristics of each Distributed LAN network. (When using netperf,
on a system with multiple NICs, take care to specify the right IP
addresses in order to ensure the network being tested is the one you
will be running Distributed LAN over. For example, if netperf -t TCP_RR
reports less than 15,000 transactions per second capacity, a
performance penalty might be incurred. Multiple copies of netperf can
also be run in parallel to determine the performance characteristics of
multiple NICs.
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The Distributed LAN (Disk Proxy) Networks
Network Configuration
and Topology
For maximum throughput, SNFS distributed LAN can utilize multiple
NICs on both clients and servers. In order to take advantage of this
feature, each of the NICs on a given host must be on a different IP
subnetwork. (This is a requirement of TCP/IP routing, not of SNFS - TCP/
IP can't utilize multiple NICs on the same subnetwork.) An example of
this is shown in the following illustration.
Figure 1 Multi-NIC Hardware
and IP Configuration Diagram
10.0.0.35
10.0.0.34
10.0.0.33
192.168.9.33
Distributed
Distributed
Distributed
LAN
Server
S1
SAN
Switch
Switch
A
B
10.0.0.x
192.168.9.x
192.168.9.45
192.168.9.44
Distributed
Distributed
192.168.9.43
10.0.0.43
Distributed
LAN
Client
C1
10.0.0.57
10.0.0.56
10.0.0.55
Distributed
Distributed
Distributed
LAN
Client
C2
In the diagram there are two subnetworks: the blue subnetwork
(10.0.0.x) and the red subnetwork (192.168.9.x). Servers such as S1 are
connected to both the blue and red subnetworks, and can each provide
up to
2 GByte/s of throughput to clients. (The three servers shown would thus
provide an aggregate of 6 GByte/s.)
Clients such as C1 are also connected to both the blue and red
subnetworks, and can each get up to 2 GByte/s of throughput. Clients
such as C2 are connected only to the blue subnetwork, and thus get a
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Distributed LAN Servers
maximum of 1 GByte/s of throughput. SNFS automatically load-
balances among NICs and servers to maximize throughput for all clients.
Note: The diagram shows separate physical switches used for the two
subnetworks. They can, in fact, be the same switch, provided it
has sufficient internal bandwidth to handle the aggregate
traffic.
Distributed LAN Servers
Distributed LAN Servers must have sufficient memory. When a
Distributed LAN Server does not have sufficient memory, its
performance in servicing Distributed LAN I/O requests might suffer. In
some cases (particularly on Windows,) it might hang.
Refer to the StorNext Release Notes for this release’s memory
requirements.
Distributed LAN Servers must also have sufficient bus bandwidth. As
discussed above, a Distributed LAN Server must have sufficient bus
bandwidth to operate the NICs used for Distributed LAN I/O at full
speed, while at the same time operating their Fibre Channel HBAs. Thus,
Quantum strong recommends using PCI Express for Distributed LAN
Servers.
Distributed LAN Client Vs. Legacy Network Attached
Storage
StorNext provides support for legacy Network Attached Storage (NAS)
protocols, including Network File System (NFS) and Common Internet
File System (CIFS).
However, using Distributed LAN Client (DLC) for NAS connectivity
provides several compelling advantages in the following areas:
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Distributed LAN Client Vs. Legacy Network Attached Storage
• Performance
• Fault Tolerance
• Load Balancing
• Client Scalability
• Robustness and Stability
• Security Model Consistency
Performance
DLC outperforms NFS and CIFS for single-stream I/O and provides higher
aggregate bandwidth. For inferior NFS client implementations, the
difference can be more than a factor of two. DLC also makes extremely
efficient use of multiple NICs (even for single streams,) whereas legacy
NAS protocols allow only a single NIC to be used. In addition, DLC
clients communicate directly with StorNext metadata controllers instead
of going through an intermediate server, thereby lowering IOP latency.
Fault tolerance
DLC handles faults transparently, where possible. If an I/O is in progress
and a NIC fails, the I/O is retried on another NIC (if one is available). If a
Distributed LAN Server fails while an I/O is in flight, the I/O is retried on
another server (if one is running). When faults occur, applications
performing I/O will experience a delay but not an error, and no
administrative intervention is required to continue operation. These
fault tolerance features are automatic and require no configuration.
Load Balancing
Client Scalability
DLC automatically makes use of all available Distributed LAN Servers in
an active/active fashion, and evenly spreads I/O across them. If a server
goes down or one is added, the load balancing system automatically
adjusts to support the new configuration.
As the following table shows, DLC supports a significantly larger
number of clients than legacy NAS protocols:
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Windows Memory Requirements
Largest Tested Configuration
NFS
CIFS
DLC
Number of Clients Tested (via
simulation)
4
4
1000
Robustness and
Stability
The code path for DLC is simpler, involves fewer file system stacks, and is
not integrated with kernel components that constantly change with
every operating system release (for example, the Linux NFS code).
Therefore, DLC provides increased stability that is comparable to the
StorNext SAN Client.
Consistent Security
Model
DLC clients have the same security model as StorNext SAN clients. When
CIFS and NFS are used, some security models aren’t supported. (For
example, Windows ACLs are not accessible when running UNIX Samba
servers.)
Windows Memory Requirements
Beginning in version 2.6.1, StorNext includes a number of performance
enhancements that enable it to better react to changing customer load.
However, these enhancements come with a price: memory requirement.
When running on a 32-bit Windows system that is experiencing memory
pressure, the tuning parameters might need adjusting to avoid running
the system out of non-paged memory. To determine current operation,
open the Task Manager and watch the Nonpaged tag in the Kernel
Memory pane in the lower right hand corner. This value should be kept
under 200MB. If the non-paged pool approaches this size on a 32-bit
system, instability might occur.
The problem will manifest itself by commands failing, messages being
sent to the system log about insufficient memory, the fsmpm
mysteriously dying, repeated FSM reconnect attempts, and messages
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Windows Memory Requirements
being sent to the application log and cvlog.txt about socket failures with
the status code (10555) which is ENOBUFS.
The solution is to adjust a few parameters on the Cache Parameters tab
in the SNFS control panel (cvntclnt). These parameters control how
much memory is consumed by the directory cache, the buffer cache,
and the local file cache.
As always, an understanding of the customers’ workload aids in
determining the correct values. Tuning is not an exact science, and
requires some trial-and-error (and the unfortunate reboots) to come up
with values that work best in the customer’s environment.
The first is the Directory Cache Size. The default is 10 (MB). If you do not
have large directories, or do not perform lots of directory scans, this
number can be reduced to 1 or 2 MB. The impact will be slightly slower
directory lookups in directories that are frequently accessed.
Also, in the Mount Option panel, you should set the Paged DirCache
option.
The next parameters control how many file structures are cached on the
client. These are controlled by the Meta-data Cache low water mark, Meta-
data Cache high water mark and Meta-data Cache Max water mark. Each
file structure is represented internally by a data structure called the
“cvnode.” The cvnode represents all the state about a file or directory.
The more cvnodes that there are encached on the client, the fewer trips
the client has to make over the wire to contact the FSM.
Each cvnode is approximately 1462 bytes in size and is allocated from
the non-paged pool. The cvnode cache is periodically purged so that
unused entries are freed. The decision to purge the cache is made based
on the Low, High, and Max water mark values. The 'Low' default is 1024,
the 'High' default is 3072, and the 'Max' default is 4096.
These values should be adjusted so that the cache does not bloat and
consume more memory than it should. These values are highly
dependent on the customers work load and access patterns. Values of
512 for the High water mark will cause the cvnode cache to be purged
when more than 512 entries are present. The cache will be purged until
the low water mark is reached, for example 128. The Max water mark is
for situations where memory is very tight. The normal purge algorithms
takes access time into account when determining a candidate to evict
from the cache; in tight memory situations (when there are more than
'max' entries in the cache), these constraints are relaxed so that memory
can be released. A value of 1024 in a tight memory situation should
work.
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Sample FSM Configuration File
Sample FSM Configuration File
This sample configuration file is located in the SNFS install directory
under the examples subdirectory named example.cfg.
#
************************************************************
# A global section for defining file system-wide parameters.
#
# For Explanations of Values in this file see the following:
#
# UNIX Users:
man cvfs_config
# Windows Users: Start > Programs > StorNext File System >
Help >
# Configuration File Internal Format
#
************************************************************
GlobalSuperUser
Yes
## Must be set to Yes for SNMS
Managed File Systems ##
WindowsSecurity
Quotas
FileLocks
DataMigration
Only ##
No
No
No
No
## SNMS Managed File Systems
InodeExpandMin
InodeExpandInc
InodeExpandMax
FsBlockSize
JournalSize
AllocationStrategy
MaxConnections
Debug
32K
128K
8M
16K
16M
Round
32
0x0
MaxLogSize
MaxLogs
4M
4
#
# Globals Defaulted
#
# ThreadPoolSize
per thread
# InodeCacheSize
default 32K
64 # default 16, 2 MB memory
32K # 800-1000 bytes each,
64M # default 32MB
# BufferCacheSize
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Sample FSM Configuration File
# StripeAlignSize
MAX(StripeBreadth)
# OpHangLimitSecs
2M # auto alignment, default
300 # default 180 secs
# DataMigrationThreadPoolSize 128 # Managed only, default 8
#
************************************************************
# A disktype section for defining disk hardware parameters.
************************************************************
[DiskType MetaDrive] ##1+1 Raid 1 Mirrored Pair##
Sectors XXXXXXXX
"cvlabel -l" ##
SectorSize 512
## Sectors Per Disk From Command
[DiskType JournalDrive] ##1+1 Raid 1 Mirrored Pair##
Sectors XXXXXXXX
SectorSize 512
[DiskType VideoDrive] ##8+1 Raid 5 Lun for Video##
Sectors XXXXXXXX
SectorSize 512
[DiskType AudioDrive] ##4+1 Raid 3 Lun for Audio##
Sectors XXXXXXXX
SectorSize 512
[DiskType DataDrive] ##4+1 Raid 5 Lun for Regular Data##
Sectors XXXXXXXX
SectorSize 512
#
************************************************************
# A disk section for defining disks in the hardware
configuration.
************************************************************
[Disk CvfsDisk0]
Status UP
Type MetaDrive
[Disk CvfsDisk1]
Status UP
Type JournalDrive
[Disk CvfsDisk2]
Status UP
Type VideoDrive
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Sample FSM Configuration File
[Disk CvfsDisk3]
Status UP
Type VideoDrive
[Disk CvfsDisk4]
Status UP
Type VideoDrive
[Disk CvfsDisk5]
Status UP
Type VideoDrive
[Disk CvfsDisk6]
Status UP
Type VideoDrive
[Disk CvfsDisk7]
Status UP
Type VideoDrive
[Disk CvfsDisk8]
Status UP
Type VideoDrive
[Disk CvfsDisk9]
Status UP
Type VideoDrive
[Disk CvfsDisk10]
Status UP
Type AudioDrive
[Disk CvfsDisk11]
Status UP
Type AudioDrive
[Disk CvfsDisk12]
Status UP
Type AudioDrive
[Disk CvfsDisk13]
Status UP
Type AudioDrive
[Disk CvfsDisk14]
Status UP
Type DataDrive
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Sample FSM Configuration File
[Disk CvfsDisk15]
Status UP
Type DataDrive
[Disk CvfsDisk16]
Status UP
Type DataDrive
[Disk CvfsDisk17]
Status UP
Type DataDrive
#
************************************************************
# A stripe section for defining stripe groups.
#***********************************************************
[StripeGroup MetaFiles]
Status UP
MetaData Yes
Journal No
Exclusive Yes
Read Enabled
Write Enabled
StripeBreadth 256K
MultiPathMethod Rotate
Node CvfsDisk0 0
[StripeGroup JournFiles]
Status UP
Journal Yes
MetaData No
Exclusive Yes
Read Enabled
Write Enabled
StripeBreadth 256K
MultiPathMethod Rotate
Node CvfsDisk1 0
[StripeGroup VideoFiles]
Status UP
Exclusive Yes##Exclusive StripeGroup for Video Files Only##
Affinity VidFiles
Read Enabled
Write Enabled
StripeBreadth 4M
MultiPathMethod Rotate
Node CvfsDisk2 0
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Sample FSM Configuration File
Node CvfsDisk3 1
Node CvfsDisk4 2
Node CvfsDisk5 3
Node CvfsDisk6 4
Node CvfsDisk7 5
Node CvfsDisk8 6
Node CvfsDisk9 7
[StripeGroup AudioFiles]
Status UP
Exclusive Yes##Exclusive StripeGroup for Audio File Only##
Affinity AudFiles
Read Enabled
Write Enabled
StripeBreadth 1M
MultiPathMethod Rotate
Node CvfsDisk10 0
Node CvfsDisk11 1
Node CvfsDisk12 2
Node CvfsDisk13 3
[StripeGroup RegularFiles]
Status UP
Exclusive No##Non-Exclusive StripeGroup for all Files##
Read Enabled
Write Enabled
StripeBreadth 256K
MultiPathMethod Rotate
Node CvfsDisk14 0
Node CvfsDisk15 1
Node CvfsDisk16 2
Node CvfsDisk17 3
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Sample FSM Configuration File
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