Users Guide

Controllers may also have dierences in their read, write, and cache policies as well as how they handle hot spares. You should be
aware of these dierences when creating virtual disks and assigning hot spares.
The following describes some of the RAID controller features and provides links to a more detailed explanation. For information on
the features supported by the controllers, see Supported Features.
• Hot spares — On RAID controllers, a hot spare is a backup for a disk that fails. See Protecting Your Virtual Disk With A Hot
Spare.
• Rebuilding data — You can rebuild data from a failed physical disk if the disk is a member of a redundant virtual disk. See
Rebuilding Redundant Information.
• Virtual disk expansion — Virtual disk expansion enables you to expand the capacity of a virtual disk while it remains online by
adding additional disks to the virtual disk. This feature is also known as online capacity expansion (OLCE). See Virtual Disk Tasks.
• RAID migration — After creating a virtual disk, you can change the RAID level. See Reconguring Or Migrating Virtual Disks.
• Moving physical and virtual disks to another controller — This feature enables you to move the physical and virtual disks from
one system to another. See Moving Physical And Virtual Disks From One System To Another.
• Read, write, and cache policies — The manner in which a controller reads and writes data can vary. The read, write, and cache
policies have implications for data encryption and system performance. See RAID Controller Read, Write, Cache, And Disk Cache
Policy.
• Check consistency — A check consistency determines the integrity of the redundant data on a virtual disk. When necessary, this
feature rebuilds the redundant information. See Maintaining The Integrity Of Redundant Virtual Disks.
• Patrol Read — Patrol read identies disk errors to avoid disk failures, data loss, or corruption. For more information, see Setting
The Patrol Read Mode.
• Disk migration or foreign congurations — Some controllers enable you to move physical disks that contain one or more virtual
disks to another controller. The receiving controller is able to recognize and import the foreign conguration (virtual disks). For
more information, see Foreign Conguration Operations.
Controller — Supported RAID Levels
RAID controllers may support dierent RAID levels. For information on supported RAID levels for a controller, see Supported
Features.
Controller — Supported Stripe Sizes
When creating a virtual disk, you must specify the stripe size for the virtual disk. Dierent controllers have dierent limitations on the
stripe sizes they can support. For information on the supported stripe sizes for a controller, see the virtual disk specications section
for the controller in Supported Features.
RAID Controller Read, Write, Cache, And Disk Cache Policy
When creating a virtual disk, you can specify the read, write, and cache policies for the virtual disk. The following subsection
describes these policies.
Related links
Changing The Virtual Disk Policy
Read Policy
Does my controller support this feature? See Supported Features.
The read policies indicate whether the controller should read sequential sectors of the virtual disk when seeking data.
• Read Ahead — The controller reads sequential sectors of the virtual disk when seeking data. Read ahead policy may improve
system performance if the data is written to the sequential sectors of the virtual disk.
• No Read Ahead — Selecting no read ahead policy indicates that the controller should not use read ahead policy.
• Read Cache Enabled — The controller reads the cache information to verify if the requested data is available in the cache
before retrieving the data from the disk. Reading the cache information rst can provide faster read performance because the
data (if available in the cache) can be retrieved more quickly from the cache than from the disk.
• Read Cache Disabled — The controller retrieves data directly from the disk and not from the cache.
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