Dell PowerEdge RAID
Controller Cards
H700 and H800
Technical Guide
Enterprise-class
controllers
designed for
performance,
reliability, and
fault tolerance.
Dell
Table of Contents
New Features...................................................................................................9
Product Support.............................................................................................. 11
PowerEdge™ Server Support.......................................................................... 11
Product Overview............................................................................................ 13
Non-Volatile Cache............................................................................... 17
Physical Disk Hot Swapping........................................................................... 18
4.10 Virtual Disk Write Cache Policies .................................................................... 20
4.11 Virtual Disk Read Cache Policies..................................................................... 20
RAID Overview................................................................................................ 21
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Tables
Figures
Figure 1. PERC H700 Integrated (Additional Sled for PCIe Slot) ...........................................6
Figure 2. PERC H700 Modular ...................................................................................7
Figure 3. PERC H800 Adapter ...................................................................................8
Figure 4. Example of RAID 0 .................................................................................. 22
Figure 5. Example of RAID 1 (Mirroring)..................................................................... 23
Figure 6. Example of RAID 5 (Single Virtual Disk with 5 drives).......................................... 24
Figure 7. Example of RAID 6 (Single Virtual Disk with 5 drives).......................................... 25
Figure 8. Example of RAID 10 (1 + 0) ........................................................................ 26
Figure 9. Example of RAID 50 (5 + 0) ........................................................................ 27
Figure 10. Example of RAID 60 (6 + 0) ........................................................................ 28
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1 Product Comparison
1.1 Overview
The PERC H700 (internal) and PERC H800 (external) RAID controllers mark the next stage in the
evolution of the Dell™ PowerEdge™ RAID controller portfolio with the introduction of 6Gb/s SAS (SAS
2.0). PERC H700 and H800 will be supported in PowerEdge 11th Generation servers. The PERC H700 is
follow-on to the PERC 6/I, and the PERC H800 is the follow-on to the PERC 6/E.
Table 1. Comparison of PERC H700 and PERC H800 to previous PERC 6/I and PERC 6/E
NEW
NEW
Feature/Spec
PERC 6/I
PERC 6/E
PERC H700
PERC H800
Interface
6Gb (SAS 2.0)
x8 PCIe 2.0
3Gb (SAS 1.1)
x8 PCIe 1.0
6Gb (SAS 2.0)
x8 PCIe 2.0
3Gb (SAS 1.1)
x8 PCIe 1.0
Bus support
Ports / Channels
8 (2 x4)
8 (2 x4)
8 (2 x4)
8 (2 x4)
2 internal
Int/Ext
Connectors
2 internal
2 external
2 external
512MB TBBU
512MB TNVC
1GB TNVC
512MB BBU 512MB
Non-Volatile
Cache
256MB
256MB / 512MB
(667 MHz DDR2)
Cache Memory
(667 MHz DDR2)
(800 MHz DDR2)
(800 MHz DDR2)
Yes
Yes
Battery-Backed
Cache
Yes
Yes
Transportable
Transportable
0, 1, 5, 6, 10, 50,
60
0, 1, 5, 6, 10, 50,
60
0, 1, 5, 6, 10, 50,
60
0, 1, 5, 6, 10, 50,
60
RAID Levels
Max physical
drives in Large
RAID volume
(R10, R50, R60)
192
144
16
10
(8x MD1220)
(6x MD1120)
HDD Support
SSD Support
SAS and SATA
SAS and SATA
SAS and SATA
SATA
SAS only
SAS only
SAS and SATA
Not Supported
Yes (Local Key
Management)
Yes (Local Key
Management)
SED Support
Not Supported
Not Supported
Controller
Firmware
7.1
6.2
7.1
6.2
(latest rev)
Redundant Path
No
No
No
No
No
No
Yes
Yes
No
Yes
Yes
No
I/O Load
Balancing
Cluster Support
Storage
Management
OpenManage™ 6.2 OpenManage™ 5.4 OpenManage™ 6.2 OpenManage™ 5.4
(minimum rev) (minimum rev) (minimum rev) (minimum rev)
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1.2 PERC H700 Overview
The PERC H700 internal host-RAID product offers three different models to support 11th Generation
Dell PowerEdge servers:
The PERC H700 Integrated card with two x4 internal mini-SAS ports supports the PCIe 2.0 x8
host interface. Cache options include standard 512 MB with battery backup unit (BBU), 512 MB
non-volatile (NV) cache, or 1 GB non-volatile cache. The PERC H700 Integrated card is
PERC H700 Integrated card.
The PERC H700 Adapter with two x4 internal mini-SAS ports supports the PCIe 2.0 x8 host
interface. Cache options include standard 512 MB with BBU, 512 MB non-volatile cache, or
1 GB non-volatile cache. The PERC H700 Adapter is installed in a PCIe slot in the server. See
Figure 1 for a view of the PERC H700 Integrated card (adapter version is the same with the
addition of a sled for adhering to the PCIe slot connection).
The PERC H700 Modular card with one x4 internal SAS port and a BBU supports the PCIe 2.0 x4
host interface. The PERC H700 Modular card is installed in the integrated slot in the blade
Figure 1. PERC H700 Integrated (Additional Sled for PCIe Slot)
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Figure 2. PERC H700 Modular
1.3 PERC H800 Overview
The PERC H800 external host-RAID product is supported with 11th Generation Dell PowerEdge servers
for expanding storage to the Dell™ PowerVault™ MD1200 and MD1220 6Gb/s SAS enclosures.
The PERC H800 Adapter with two x4 external mini-SAS ports supports the PCIe 2.0 x8 host interface.
Cache options include the standard 512 MB transportable battery backup unit (TBBU) and the
transportable 512 MB and 1 GB non-volatile cache. The PERC H800 Adapter is installed in a PCIe slot
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2 New Features
2.1 Overview
The PERC H700 and PERC H800 offer the new CacheCade feature:
• Produces cost-effective performance scaling for database-type applications
• Offloads Random Reads to Dell-qualified Enterprise SSD configured as CacheCade SSD
• Has a standard feature of 1 GB NV cache (PERC H700/H800)
The PERC H700 and PERC H800 continue to offer the following features:
• 512 MB and 1 GB non-volatile cache (not supported on H700 modular)
o
Data retention in cache is extended from hours to years in the event of power
interruption
Larger cache size of 1 GB
o
•
Cut-through IO (CTIO)
o
o
o
o
Performance boost of up to 2X IOPS performance
Optimized for superior IOPS of SSDs over HDDs
Ideal for small-block random workloads
Easy to enable
• Physical disk power management
o
o
Conserve power by spinning down hot spares and unconfigured drives when not in use
Parameters are user-managed
• PCI-Express Gen2.0 support
• 6Gb/s SAS (SAS 2.0) host interface
o
o
Doubles the throughput performance
Support for Self Encrypting Drive (SED)—requires unique SED HDD part numbers
• New LSI 2108 ROC (Raid-on-Chip) with increased I/O processor (IOP) performance
• Increased internal drive support (up to 16 drives)
• SAS SSD support for specific 11th Generation Dell PowerEdge servers
• RAID volumes can be migrated from PERC 6/I, PERC 6/E, SAS 6/IR and PERC H200 controllers.
Backwards migration is not supported.
• Change in Virtual Disk default read cache policy (The default VD read cache policy has been
changed to Adaptive Read Ahead from No Read Ahead.)
• Display of expected and negotiated link rate for drives
The PERC H800 also offers the following features for PowerVault MD1200 and MD1220 enclosures:
• Increased capacity and scalability—up to 192 drives on one host-RAID controller
• Increased flexibility
o
o
Mix of 2.5” (MD1220) and 3.5” (MD1200) enclosures behind a PERC H800
Mix of 2.5” and 3.5” drives in the MD1200
• SAS SSD support for Dell PowerVault MD1200 and MD1220 enclosures
• 22-drive RAID-10 can be configured with PERC H800 in the CTRL-R BIOS utility
2.2 6Gb/s SAS (SAS 2.0) Overview
The 6Gb/s SAS 2.0 specification doubles the current 3Gb/s SAS data transfer rate. 6Gb/s SAS is
designed for backward compatibility with 3Gb/s SAS and 3Gb/s SATA hard drives. Regardless of the
drive speed, 6Gb/s controllers will deliver significant performance improvements in both read and
write applications as compared to their 3Gb/s predecessors.
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Other new features of the 6Gb/s SAS controllers will offer improved signal integrity and additional
safeguards to enhance data protection with support for SED (Self-Encrypting Drive) technology.
Table 2. 6Gb/s SAS (SAS 2.0) Features
DAS-based
Server Storage
6Gb/s Throughput
3Gb/s Compatible
Standard Mini-SAS Connectors (SFF-8087
and SFF-8088)
DFE (Decision Feedback Equalization)
improved signaling
SSC (Spread Spectrum Clocking) reduced
radiated emissions
Enhanced Security with SED (Self-
Encrypting Drive) support
Improved Scalability
2.2.1
6Gb/s SAS Performance Benefit over 3Gb/s SAS
In small disk drive configurations (one to eight drives) the aggregate media rate of the disks (the
speed at which the disk heads can read and write data) become the bottleneck for storage
throughput. As business storage needs grow, IT centers can add more disk drives to their storage
infrastructure, and the latest generation of SAS allows server performance to scale past the 3Gb/s
SAS performance limitations: from 2.4 GB/s to 4.8 GB/s unidirectional.
Table 3. SAS Performance Details
SAS Generation
PCI-Express
Interface
Approximate number of SAS
HDDs required saturate
bandwidth (RAID 0)
1.0 (3Gb)
2.0 (6Gb)
1.0
2.0
8 to10
16 to 20
In addition to the improvements in the SAS bandwidth, PCI Express 2.0 provides double the system-
to-storage controller interconnect speed. The x8 PCI Express 1.0 interface linking the controller to
the host platform limited throughput even further to a theoretical 2GB/s maximum, that limitation
has been raised to 4GB/s (unidirectional).
2.2.2
6Gb/s SAS Expectation
RAID controllers employing 6Gb/s SAS technology excel in both high IOP and high bandwidth
applications. Applications and environments that benefit most range from traditional data center
applications (such as random IOPs intensive email, web and database servers) to streaming and
archival applications that will benefit from improved sequential read and write throughput. This
means more users, more video streams, more email accounts, and faster backups are now possible.
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3 Product Support
3.1 Dell PowerEdge Server Support
The Dell PERC H700 and PERC H800 are supported with 11th Generation Dell™ PowerEdge™ servers.
H800. For the latest Dell PERC support matrix with Dell PowerEdge servers, visit the PERC web page
Table 4. PowerEdge Server Support with PERC H700 and PERC H800
PERC H700 Internal PERC H700
PERC H700 Internal PERC H800 External
Internal
Integrated
Modular
Adapter
Adapter
R510
R610
T610
R710
T710
R715
R810
R815
R910
R310
T310
R410
T410
M610
M610x
M710
M910
T310
R310
R410
T410
R510
R610
T610
M610x
R710
T710
R715
R810
R815
R910
3.2 Management Software Support
The Dell PERC H700 and H800 are supported with 11th Generation Dell PowerEdge servers and
managed through common Dell OpenManage™ Storage Management software (minimum version 6.2).
For pre-OS configuration, the PERC BIOS utility can also be used to configure and troubleshoot the
PERC H700 and PERC H800 products.
3.3 Operating System Support
The Dell PERC H700 and PERC H800 provide operating system support based on Dell 11th Generation
PowerEdge support requirements as shown in Error! Reference source not found.. For the latest list
of supported operating systems and driver installation instructions, see the system documentation on
the Dell Support website at support.dell.com/manuals. For specific operating system service pack
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Table 5. Operating System Support with PERC H700 and PERC H800
Supported Operating Systems
Microsoft® Windows Server® 2003 Family
Microsoft Windows Server 2008 Family
Microsoft Windows Server 2008 R2
Red Hat® Enterprise Linux® Version 4 and Version 5
RHEL 4.7 and later (32 and 64 bit)
RHEL 5.3 and later (32 and 64 bit)
Sun® Solaris™ 10 (64-bit)
Novell® SUSE® Linux® Enterprise Server Version 10 (64-bit) and Version 11 (64-bit)
SLES10 SP2 and later
SLES11 GM and later
VMware® vSphere™ 4.1 (including VMware ESX® 4.1 or VMware ESXi™ 4.1)
Support Matrix for Dell PowerEdge Systems on Dell.com.
3.4 Drive Support
The Dell PERC H700 supports SAS and SATA interface drives, both HDD (hard-disk drive) and SSD
(solid-state drive). The Dell PERC H800 supports SAS interface drives, both HDD and SSD. Refer to the
following table for drive support details. For specific form-factor and capacity support, see the
Non Dell certified drives will be blocked. For more information on the benefits of using Dell certified
Table 6. Drive Support
Drive Type
HDD
Interface
PERC H700
PERC H800
6Gb/s SAS
Yes
Yes
3Gb/s SAS
Yes
Yes
3Gb/s SATA
3Gb/s SAS
Yes
Yes
Yes
No
Yes
No
SSD
3Gb/s SATA
SATA interface drives are not supported with PERC H800 and the Dell PowerVault MD1200 and
MD1220 enclosures.
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Feature
PERC H700
PERC H700 Modular
PERC H800 Adapter
Integrated/Adapter
Physical Disk
Power
Yes
Yes
Yes
Management
RAID Level
Migration
Yes
Yes
Yes
Yes
Yes
Yes
On-line Capacity
Expansion
Non-Volatile Cache Yes
No
Yes
Yes
Yes
SMART Support
Yes
Yes
N/A
Redundant Path
Support
N/A
Dedicated and
Global Hot Spares
Yes
Yes
Yes
Yes
Yes
Yes
Revertible Hot
Spares
Hot Swap Devices
Disk Roaming
Disk Migration
SED Support
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Mixed Capacity
Physical Drive
Enclosures per
Port
N/A
N/A
N/A
Up to 4 per port
(total of 8 enclosures
per Adapter)
Enclosure Hot-Add N/A
Yes
SAS port
LEDs used to determine
Supported.
connection LED
the status of the SAS
port
Port State; LED State
Power On State; Off
Reset State; Off
All links in port
Connected; Green On
1 or more links not
connected (only
applicable in wide port
configurations); Amber
On
All links in port
disconnected or Cable
disconnected; Off
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Feature
PERC H700
PERC H700 Modular
PERC H800 Adapter
Integrated/Adapter
Clustering
Card and software
stack enables High
Availability Clusters
Not supported
4.2 CacheCade
CacheCade provides cost-effective performance scaling for database-type application profiles in a
host-based RAID environment by extending the PERC RAID controller cache with the addition of Dell-
qualified Enterprise SSDs.
CacheCade identifies frequently-accessed areas within a data set and copies this data to a Dell-
qualified, Enterprise SSD (SATA or SAS), enabling faster response time by directing popular Random
Read queries to the CacheCade SSD instead of to the underlying HDD.
Supporting up to 512 GB of extended cache, CacheCade SSDs must all be the same interface (SATA or
SAS) and will be contained in the server or storage enclosure where the RAID array resides.
CacheCade SSDs will not be a part of the RAID array.
CacheCade is a standard feature on, and only available with, the PERC H700/H800 1 GB NV Cache
RAID controller.
CacheCade SSDs can be configured using the PERC BIOS Configuration Utility or OpenManage.
4.3 Cut-Through IO
Cut-through IO (CTIO) is an IO accelerator for SSD arrays that boosts the throughput of devices
connected to the PERC Controller. It is enabled through disabling the write-back cache (enable
write-through cache) and disabling Read Ahead.
4.4 Reconfiguring Virtual Disks
There are two methods to reconfigure RAID virtual disks—RAID Level Migration (RLM) and Online
Capacity Expansion (OCE). RLM involves the conversion of a virtual disk to a different RAID level. OCE
refers to increasing the capacity of a virtual disk, which can be accomplished in three ways:
If there is a single virtual disk in a disk group and free space is available, the virtual disk’s
capacity can be expanded within that free space. If a virtual disk is created and it does not use
the maximum size of the disk group, free space is available.
Free space is also available when a disk group’s physical disks are replaced by larger disks using
the Replace Member feature.
A virtual disk's capacity can also be expanded by performing an OCE operation to add more
physical disks by encompassing all available free space on a given virtual disk, adding drives
and/or migrating to a different RAID level.
When a RLM/OCE operation is complete, a reboot is not necessary. For a list of RAID level migrations
and capacity expansion possibilities, see Table 1. The source RAID level column indicates the virtual
disk level before the RAID level migration and the target RAID level column indicates the RAID level
after the operation is complete. If you configure 64 virtual disks on a controller, you cannot perform
a RAID level migration or capacity expansion on any of the virtual disks. The controller changes the
write cache policy of all virtual disks undergoing a RLM/OCE to Write-Through until the RLM/OCE is
complete.
Note: RAID level migration and expansion is not supported on RAID levels 10, 50, and 60.
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Table 8. RAID Level Migration
Source RAID
Level
Target RAID
Level
# of Physical
Drives
(Beginning)
# of Physical
Drives (End)
Capacity
Expansion
Possible
Description
RAID 0
RAID 1
1
2
No
Converting non-
redundant virtual disk
into a mirrored virtual
disk by adding one drive.
RAID 0
RAID 0
RAID 1
RAID 5
RAID 6
RAID 0
1 or more
1 or more
2
3 or more
4 or more
2 or more
Yes
Yes
Yes
At least one drive needs
to be added for
distributed parity data.
At least two drives need
to be added for dual
distributed parity data.
Removes redundancy
while increasing
capacity.
RAID 1
RAID 1
RAID 5
RAID 6
2
2
3 or more
4 or more
Yes
Yes
Maintains redundancy
while doubling capacity.
Two drives are required
to be added for
distributed parity data.
RAID 5
RAID 0
3 or more
3 or more
Yes
Converting to a non-
redundant virtual disk
and reclaiming disk space
used for distributed
parity data.
RAID 5
RAID 6
RAID 6
RAID 0
3 or more
4 or more
4 or more
4 or more
Yes
Yes
At least one drive needs
to be added for dual
distributed parity data.
Converting to a non-
redundant virtual disk
and reclaiming disk space
used for distributed
parity data.
RAID 6
RAID 5
4 or more
4 or more
Yes
Removing one set of
parity data and
reclaiming disk space
used for it.
4.5 Fault-Tolerance Features
Below is a list of features that provide fault tolerance to prevent data loss:
Non-volatile cache: extends data retention from hours to years
Support for SMART
Redundant path support (for PERC H800 only)
Physical disk failure detection
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Physical disk rebuild using hot spares
Enclosure affinity
Parity generation and checking (for RAID 5, 50, 6, and 60 only)
Battery backup of controller cache to protect data
Detection of batteries with low charge after boot up
4.5.1
Non-Volatile Cache
Dell PERC controllers with non-volatile (NV) cache use the standard battery as contained in the Dell
PERC controllers with a battery back-up unit (BBU). The difference is in battery implementation:
The battery in the BBU offering retains the data in cache in the event of a power cycle for a
guaranteed period of 24 hours (typically up to 72 hours).
The battery in the NV cache offering will transfer the data from cache to flash in the event of
a power cycle, where the data will be retained for up to ten years.
4.5.2
Automatic Replace Member with Predicted Failure
A Replace Member operation can occur when there is a SMART predictive failure reporting on a drive
in a virtual disk. The automatic Replace Member is initiated when the first SMART error occurs on a
physical disk that is part of a virtual disk. The target drive needs to be a hot spare that qualifies as a
rebuild drive. The physical disk with the SMART error is marked as failed only after the successful
completion of the Replace Member. This avoids putting the array in degraded status. If an automatic
Replace Member occurs using a source drive that was originally a hot spare (that was used in a
rebuild), and a new drive added for the Replace Member operation as the target drive, the hot spare
reverts to the hot spare state after a successful Replace Member operation. To enable the automatic
Replace Member, use the Dell OpenManage storage management application.
4.5.3
Redundant Path with Load Balancing Support
The PERC H800 adapter can detect and use redundant paths to drives contained in enclosures. This
provides the ability to connect two SAS cables between a controller and an enclosure for path
redundancy. The controller is able to tolerate the failure of a cable or Enclosure Management
Module (EMM) by using the remaining path. When redundant paths exist, the controller automatically
balances I/O load through both paths to each disk drive. This load balancing feature increases
throughput to each drive and is automatically turned on when redundant paths are detected. To set
up your hardware to support redundant paths, see the Setting up Redundant Path Support on the
PERC H800 Adapter section in the PERC H700 and PERC H800 User’s Guide
4.5.4
Failed Physical Disk Detection
The controller automatically detects and rebuilds failed physical disks when you place a new drive in
the slot where the failed drive resided or when an applicable hot spare is present. Automatic
rebuilds can be performed transparently with hot spares. If you have configured hot spares, the
controllers automatically try to use them to rebuild failed physical disks.
4.5.5
Using Replace Member and Revertible Hot Spares
The Replace Member functionality allows a previously commissioned hot spare to be reverted back to
a usable hot spare. When a drive failure occurs within a virtual disk, an assigned hot spare
(dedicated or global) is commissioned and begins rebuilding until the virtual disk is optimal. After the
failed drive is replaced (in the same slot) and the rebuild to the hot spare is complete, the controller
automatically starts to copy data from the commissioned hot spare to the newly inserted drive. After
the data is copied, the new drive is part of the virtual disk and the hot spare is reverted back to
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being a ready hot spare. This allows hot spares to remain in specific enclosure slots. While the
controller is reverting the hot spare, the virtual disk remains optimal. The controller automatically
reverts a hot spare only if the failed drive is replaced with a new drive in the same slot. If the new
drive is not placed in the same slot, a manual Replace Member operation can be used to revert a
previously commissioned hot spare.
4.5.6
Enclosure Affinity
Enclosure affinity is used to set the preference for a hot spare to be used to rebuild a physical disk
that resides in the same physical enclosure. This does not preclude the hot spare from being
provisioned to a second enclosure if there are no other hot spares present. For example, if there are
two enclosures and each enclosure has a hot spare with affinity set, then upon a drive failure the hot
spare will be provisioned from the same enclosure as the failed drive.
Hot-spare enclosure affinity can be configured only if you are using an external storage enclosure.
4.5.7
Battery Back-up of Controller Cache
Battery Management
4.5.7.1
The transportable battery backup unit (TBBU) is a cache memory module with an integrated battery
pack that enables you to transport the cache module with the battery in a new controller. The TBBU
protects the integrity of the cached data on the PERC H800 adapter by providing backup power
during a power outage. The battery backup unit (BBU) is a battery pack that protects the integrity of
the cached data on the PERC H700 cards by providing backup power during a power outage. The
battery provides up to 24 hours of backup power for the cache memory.
4.5.7.2
Battery Learn Cycle
Learn cycle is a battery calibration operation performed by the controller periodically to determine
the condition of the battery. This operation cannot be disabled.
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4.7 Disk Roaming
The PERC H700 and H800 cards support moving physical disks from one cable connection or
backplane slot to another on the same controller. The controller automatically recognizes the
relocated physical disks and logically places them in the proper virtual disks that are part of the disk
group. Disk roaming can be performed only when the system is turned off. Disk roaming should not
be performed during RAID level migration (RLM) or online capacity expansion (OCE). This causes loss
of the virtual disk.
4.8 Disk Migration
The PERC H700 and H800 cards support migration of virtual disks from one controller to another
without taking the target controller offline. However, the source controller must be offline prior to
performing the disk migration. The controller can import RAID virtual disks in optimal, degraded, or
partially degraded states. A virtual disk cannot be imported if it is in an offline state.
Disks cannot be migrated back to previous PERC RAID controllers. When a controller detects a
physical disk with an existing configuration, it flags the physical disk as foreign, and it generates an
alert indicating that a foreign disk was detected. Disk roaming should not be used during RLM or
online capacity expansion OCE as it can cause loss of the virtual disk.
Virtual disks that are created on the PERC 6 and H200 family of controllers can be migrated to the
PERC H700 and H800 controllers without risking data or configuration loss. Migrating virtual disks
from the PERC H700 and H800 cards to PERC 6 or PERC H200 is not supported.
During the discharge phase of a learn cycle, the PERC H700 or H800 battery charger is disabled and
remains disabled until the battery is discharged. After the battery is discharged, the charger is re-
enabled.
4.9 PERC H700 and H800 Security Key and RAID Management
4.9.1
PERC H700 and H800 Security Key Implementation
The Dell PowerEdge RAID Controller (PERC) H700 and H800 cards support encryption of data on the
drives when using Dell qualified self-encrypting drives (SEDs). This feature provides protection to the
data at rest in the event of theft or loss of drives. There is one security key per controller which
resides in the controller memory and it can be managed by the user (local key management). The
security key is used by the controller to lock and unlock access to encryption-capable physical drives.
In order to take advantage of this feature, you need to create a security key on your PERC H700 or
PERC H800 controller and have Dell qualified SEDs.
4.9.2
Configuring and Managing Secured RAID
Dell OpenManage storage management applications enable you to create and manage a security key,
manage and configure the RAID system, create and manage multiple disk groups, control and monitor
multiple RAID systems, and provide online maintenance. The management applications for PERC
H700 and H800 include:
• Dell OpenManage Storage Management
• BIOS Configuration Utility
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4.10 Virtual Disk Write Cache Policies
The write cache policy of a virtual disk determines how the controller handles writes to that virtual
disk. Write-Back and Write-Through are the two write cache policies and can be set on virtual disks
individually.
All RAID volumes will be presented as Write-Through (WT) to the operating system (Windows and
Linux) independent of the actual write cache policy of the virtual disk. The PERC cards manage the
data in cache independently of the operating system or any applications. You can use OpenManage or
the BIOS configuration utility to view and manage virtual disk cache settings.
In Write-Through caching, the controller sends a data-transfer completion signal to the host system
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5 RAID Overview
5.1 About RAID
RAID is a way of storing data on multiple independent physical disks for the purpose of enhanced
performance and/or fault tolerance. The physical disks combine to make up what is called a virtual
disk. This virtual disk appears to the host system as a single logical unit or drive. For example, if you
have physical disk 1 and physical disk 2 forming a RAID virtual disk, those two disks appear to the
host system as one disk.
Virtual Disks are sometimes called volumes, containers, or arrays.
There are several different RAID types or levels, which determine how the data is placed in the
virtual disk. Each RAID level has specific data protection and system performance characteristics.
The following are commonly used RAID levels:
• RAID 0: Striping without parity, improved performance, additional storage, no fault tolerance
• RAID 1: Mirroring without parity, fault tolerance for disk errors, and single disk failures
• RAID 5: Striping with distributed parity, improved performance, fault tolerance for disk
errors, and single disk failures
• RAID 6: Striping with dual parity, fault tolerance for dual drive failures
• RAID 10: Mirroring combined with striping, better performance, fault tolerance for disk
errors, and multiple drive failure (one drive failure per mirror set)
• RAID 50: Combines multiple RAID 5 sets with striping, improved performance, fault disk
errors, and multiple drive failures (one drive failure per span)
• RAID 60: Combines multiple RAID 6 sets with striping, improved performance, fault disk
errors, and multiple drive failures (two drive failures per span)
These RAID levels are discussed in more detail later in this document. You can manage RAID virtual
disks with a RAID controller (hardware RAID) or with software (software RAID).
5.2 Advantages of RAID
Depending on how you implement RAID, the benefits include one or both of the following:
• Faster performance—In RAID 0, 10, 50, or 60 virtual disks, the host system can access
simultaneously. This improves performance because each disk in a virtual disk has to handle
the request. For example, in a two-disk virtual disk, each disk needs to provide only its
requested data.
• Data protection—In RAID 1, 10, 5, 6, 50, and 60 virtual disks, the data is backed up on disk
(mirror). In the RAID 5, 50, 6, or 60 virtual disks, the data is also parity protected. RAID 10,
50, and 60 also allow the host to access disks simultaneously.
5.3 Supported RAID Levels
Dell servers that use RAID controllers may support RAID 0, 1, 5, 6, 10, 50, and 60 depending upon the
controller. The following is a brief explanation of these levels.
5.3.1
RAID 0 (Striped Virtual Disk without Fault Tolerance)
RAID 0, also known as striping, maps data across the physical drives to create a large virtual disk.
The data is divided into consecutive segments or stripes that are written sequentially across the
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For example, a four-drive virtual disk may be configured with 16 stripes (four stripes of designated
space per drive). Stripes A, B, C and D are located on corresponding hard drives 0, 1, 2, and 3. Stripe
E, however, appears on a segment of drive 0 in a different location than stripe A; stripes F through H
appear accordingly on drives 1, 2 and 3. The remaining eight stripes are allocated in the same even
fashion across the drives.
RAID 0 provides improved performance because each drive in the virtual disk needs to handle only
part of a read or write request. However, because none of the data is mirrored or backed up on
parity drives, one drive failure makes the virtual disk inaccessible and the data is lost permanently.
Data 4
Data 8
Data 12
Data 16
Data 1
Data 5
Data 9
Data 13
Data 2
Data 6
Data 10
Data 14
Data 3
Data 7
Data 11
Data 15
Drive 0
Drive 1
Drive 2
Drive 3
Figure 4. Example of RAID 0
Advantages of RAID 0
I/O performance is greatly improved by spreading the I/O load across many channels and
drives (best performance is achieved when data is striped across multiple channels with only
one drive per channel)
No parity calculation overhead is involved
Very simple design
Easy to implement
Disadvantages of RAID 0
Not a "true" RAID because the failure of just one drive will result in all data in a virtual disk
being lost
Should not be used for critical data unless another form of data redundancy is deployed
5.3.2
RAID 1 (Mirroring)
RAID 1 is achieved through disk mirroring to ensure data reliability or a high degree of fault
tolerance. In a RAID 1 configuration, the RAID management software instructs the subsystem's
controller to store data redundantly across a number of the drives (mirrored set) in the virtual disk.
In other words, if a disk fails, the mirrored drive takes over and functions as the primary drive.
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Data 1
Data 1
Data 2
Data 3
Data 4
Data 2
Data 3
Data 4
Drive 0
Drive 1
Figure 5. Example of RAID 1 (Mirroring)
Advantages of RAID 1
High performance up to twice the read transaction rate of single disks, and the same write
transaction rate as single disks
100 percent redundancy of data means no rebuild of data is necessary in case of disk failure,
just a copy to the replacement disk
Typically supports hot-swap disks
Simplest RAID storage subsystem design
Fastest recovery of data after a drive failure, no data has to be recreated from parity codes
on retrieval
Disadvantages of RAID 1
Highest disk overhead of all RAID types (100 percent) results in inefficient use of drive
capacity
Limited capacity since the virtual disk can only include two disk drives
5.3.3
RAID 5 (Striping With Distributed Parity)
RAID 5 maps the data across the drives and stores parity information for each data stripe on different
drives in the virtual disk. Data redundancy is maintained with a technique called parity checking.
With this technique, the RAID controller writes information called parity bits on the disks. Parity data
is distributed across disks in the RAID 5 virtual disk such that any 1 disk failure within the virtual disk
allows data to be recreated from the remaining disks.
Parity is used to maintain data integrity and to rebuild lost data in case of drive failures. Parity bit
data can be written on a single drive (this is RAID Level 3), but during periods of high write activity,
the parity disk can become saturated with writes. This reduces the server’s write throughput.
However, RAID Level 5 reduces parity write bottlenecks by allowing all of the drives in the virtual
disk to assume part of the parity responsibilities. This alleviates the single drive bottleneck,
improving overall subsystem throughput. Figure 6 shows how the parity data is distributed among five
hard drives.
A RAID 5 virtual disk can preserve data if one drive fails. However, if two drives fail, the virtual disk
will fail.
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0 parity
Data 1
Data 5
Data 3
Data 7
Data 4
1 parity
Data 11
Data 15
Data 19
Data 2
Data 6
Parity
Generation
Data 8
Data 12
Data 16
Data 20
Data 10
3 parity
Data 17
2 parity
Data 14
Data 18
Data 9
Data 13
4 parity
Drive 1
Drive 2
Drive 3
Drive 4
Drive 5
Figure 6. Example of RAID 5 (Single Virtual Disk with 5 drives)
Advantages of RAID 5
Most efficient use of drive capacity of all the redundant RAID configurations
High read transaction rate
Medium-to-high write transaction rate
Disadvantages of RAID 5
Disk failure has a medium impact on throughput
Most complex controller design
Retrieval of parity information after a drive failure takes longer than with mirroring
5.3.4
RAID 6 (Striping With Dual Distributed Parity)
RAID 6 provides data redundancy by using data striping in combination with parity information. See
Figure 7. Similar to RAID 5, the parity is distributed within each stripe. RAID 6, however, uses an
additional physical disk to maintain parity, such that each stripe in the disk group maintains two disk
blocks with parity information. The additional parity provides data protection in the event of two
disk failures.
Figure 7 depicts the RAID 6 data layout. The second set of parity drives are denoted by Q. The P
drives follow the RAID 5 parity scheme. The parity blocks on Q drives are computed using Galois Field
mathematics. There is no performance hit on read operations. However, as a second independent
parity data needs to be generated for each write operation, there is a performance hit during write.
Due to dual data protection, a RAID 6 VD can survive the loss of two drives or the loss of a drive when
one of its drives is being rebuilt.
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Figure 7. Example of RAID 6 (Single Virtual Disk with 5 drives)
Advantages of RAID 6
Can survive the loss of two disks without losing data
Data redundancy, high read rates, and good performance
Disadvantages of RAID 6
Requires two sets of parity data for each write operation, resulting in significant decrease in
write performance
Additional costs because of the extra capacity required by using two parity blocks per stripe
Retrieval of parity information after a drive failure takes longer than with mirroring
5.3.5
RAID 10 (Striping over Mirrored Sets)
RAID 10 combines striping and mirroring to produce large virtual disks with high performance and
fault-tolerance. The performance gain comes from striping across mirror sets without the need for
parity calculations. See Figure 8.
Although this delivers the highest performance, the drive storage overhead is 100 percent because
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RAID 0
RAID 1
RAID 1
Data 1
Data 3
Data 5
Data 7
Data 2
Data 4
Data 6
Data 8
Data 1
Data 3
Data 5
Data 7
Data 2
Data 4
Data 6
Data 8
=
=
Drive 0
Drive 1
Drive 2
Drive 3
Figure 8. Example of RAID 10 (1 + 0)
Advantages of RAID 10
RAID 10 has the same redundancy as RAID level 1
High I/O rates are achieved by striping RAID 1 segments
Allows creation of largest RAID group with up to 192 drives connected to PERC H800
Disadvantages of RAID 10
Most expensive RAID solution
Requires 2n where n > 1 disks
5.3.6
RAID 50 (Striping Across RAID 5)
RAID 50 is a variation of RAID 5 that maps data across two or more RAID 5 virtual disks. The RAID 5
stripes data across each RAID 5 subset. RAID 50 provides a higher degree of fault tolerance since 1
drive per RAID 5 set may fail without data being lost.
A performance increase over RAID 5 may be realized depending on the configuration due to fewer
disks reads per parity calculation.
For example, if a comparison of a RAID 5 virtual disk with 6 disks were made to a RAID 50 virtual disk
with two 3 disk RAID 5 virtual disks, the parity calculation on the RAID 10 virtual disk would require
reading all 6 disks each time, where the parity calculation on the RAID 50 may require only reading
3. This may vary depending on several factors such as cache and data block sizes.
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RAID 0
RAID 5
RAID 5
0 parity
0 parity
0 parity
0 parity
Data 3
Data 1
Data 2
Data 4
1 parity
Parity
Generation
Parity
Generation
1 parity
Data 5
2 parity
Data 6
Data 7
2 parity
Data 8
Data 11
Data 10
Data 12
Data9
Drive 1
Drive 2
Drive 3
Drive 6
Drive 5
Drive 4
Figure 9. Example of RAID 50 (5 + 0)
Advantages of RAID 50
Allows creation of largest RAID groups, up to 256 drives (theoretical; large RAID volumes are
allowed for up to 192 drives connected to PERC H800)
High read transaction rate
Higher degree of fault tolerance due to parity calculation being done for each RAID 5 subset
Potential for faster read transaction rates over large RAID 5 virtual disks
Medium-to-high write transaction rate
Disadvantages of RAID 50
Disk failure has a medium impact on throughput
One of the more complex RAID implementations
Less space efficient than RAID 5 since separate parity calculations are done for each RAID 5
subset
Retrieval of parity information after a drive failure takes longer than using a mirrored solution
5.3.7
RAID 60 (Striping Across RAID 6)
RAID 60 is striping over more than one span of physical disks that are configured as a RAID 6. The
RAID 6 subset must have at least four disks. For example, a RAID 6 disk group that is implemented
with four physical disks and then continues on with a disk group of four more physical disks would be
a RAID 60. See Figure 10.
RAID 60 stripes data across each RAID 6 subset. RAID 60 provides a higher degree of fault tolerance
since 2 drives per RAID 6 set may fail without data being lost. A performance increase over RAID 6
may be realized depending on the configuration due to fewer disks reads per parity calculation.
For example, if a comparison of a RAID 6 virtual disk with 8 disks were made to a RAID 60 virtual disk
with two 4 disk RAID 6 virtual disks, the parity calculation on the RAID 10 virtual disk would require
reading all 6 disks each time, where the parity calculation on the RAID 60 may require only reading
4. This may vary depending on several factors such as cache and data block sizes.
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Data 1
Parity
Generation
Drive 1
Drive 5
Drive 6
Drive 7
Drive 2
Drive 3
Figure 10. Example of RAID 60 (6 + 0)
Advantages of RAID 60
Allows creation of largest RAID groups, up to 256 drives (theoretical); large RAID volumes are
allowed for up to 192 drives connected to PERC H800
High degree of fault tolerance due to 2 parity calculations being done for each RAID 6 subset
Medium-to-high write transaction rate
Disadvantages of RAID 60
One of the more complex RAID implementations
Less space-efficient than RAID 6 since separate parity calculations are done for each RAID 6
subset
Retrieval of parity information after a drive failure takes longer than using a mirrored solution
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Appendix A. Additional Resources
Table 9. Resource Contact Information and Descriptions
Type Of Information URL
Description
PERC Resources
Support matrix, whitepapers,
and important links
PERC Hardware
Owner’s Manual
Specifications, feature
overview and descriptions,
installation, management, and
troubleshooting
OpenManage User
Documentation
User Guide for OMSS questions
and support
Break/Fix
www.support.dell.com (Customer
tab)
Troubleshooting issues
First contact for
product issues.
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