Avago Technologies MegaRAID Fast Path Software - Manual (Page 492)

Page 492 LSI Corporation Confidential | July 2011
MegaRAID SAS Software User Guide Appendix C: Glossary
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 LSI 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.