Lenovo ThinkServer RD330, Software User'S Manual

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Page 392
MegaRAID SAS Software User Guide Appendix C: Glossary
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consistency check An operation that verifies that all stripes in a virtual drive with a redundant RAID level
are consistent and that automatically fixes any errors. For RAID 1 drive groups, this
operation verifies correct mirrored data for each stripe.
consistency check rate The rate at which consistency check operations are run on a computer system.
controller A chip that controls the transfer of data between the microprocessor and memory or
between the microprocessor and a peripheral device such as a drive. RAID controllers
perform RAID functions such as striping and mirroring to provide data protection.
MegaRAID Storage Manager software runs on SAS controllers.
copyback The procedure used to copy data from a source drive of a virtual drive to a destination
drive that is not a part of the virtual drive. The copyback operation is often used to
create or restore a specific physical configuration for a drive group (for example, a
specific arrangement of drive group members on the device I/O buses). The copyback
operation can be run automatically or manually.
Typically, a drive fails or is expected to fail, and the data is rebuilt on a hot spare. The
failed drive is replaced with a new drive. Then the data is copied from the hot spare to
the new drive, and the hot spare reverts from a rebuild drive to its original hot spare
status. The copyback operation runs as a background activity, and the virtual drive is
still available online to the host.
current write policy A virtual drive property that indicates whether the virtual drive currently supports
Write Back mode or Write Through mode.
 In Write Back mode the controller sends a data transfer completion signal to the
host when the controller cache has received all of the data in a transaction.
 In Write Through mode the controller sends a data transfer completion signal to the
host when the drive subsystem has received all of the data in a transaction.
default write policy A virtual drive property indicating whether the default write policy is Write Through or
Write Back. In Write Back mode the controller sends a data transfer completion signal to
the host when the controller cache has received all of the data in a transaction. In Write
Through mode the controller sends a data transfer completion signal to the host when
the drive subsystem has received all of the data in a transaction.
device ID A controller or drive property indicating the manufacturer-assigned device ID.
device port count A controller property indicating the number of ports on the controller.
drive cache policy A virtual drive property indicating whether the virtual drive cache is enabled, disabled,
or unchanged from its previous setting.
drive group A group of drives attached to a RAID controller on which one or more virtual drives can
be created. All virtual drives in the drive group use all of the drives in the drive group.
drive state A drive property indicating the status of the drive. A drive can be in one of the
following states:
 Unconfigured Good: A drive accessible to the RAID controller but not configured as
a part of a virtual drive or as a hot spare.
 Hot Spare: A drive that is configured as a hot spare.
 Online: A drive that can be accessed by the RAID controller and will be part of the
virtual drive.
 Rebuild: A drive to which data is being written to restore full redundancy for a
virtual drive.
 Failed: A drive that was originally configured as Online or Hot Spare, but on which
the firmware detects an unrecoverable error.