Users Guide

RAID Controller Features
Different controllers have different features. If you have more than one controller attached to your system, you may notice that the tasks
displayed on the Information/Configuration page of the controller are different for each controller.
Controllers may also have differences in their read, write, and cache policies as well as how they handle hot spares. You should be aware
of these differences 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 Reconfiguring 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 identifies disk errors to avoid disk failures, data loss, or corruption. For more information, see Setting The
Patrol Read Mode.
• Disk migration or foreign configurations — 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 configuration (virtual disks). For more
information, see Foreign Configuration Operations.
Controller — Supported RAID Levels
RAID controllers may support different 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. Different controllers have different limitations on the
stripe sizes they can support. For information on the supported stripe sizes for a controller, see the virtual disk specifications 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.
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 first 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.
Controllers
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