User's Manual

84 Glossary
hotspare
A standby physical disk that can automatically replace a failed physical disk in a
virtual disk and prevent data from being lost. A hotspare can be dedicated to a
single redundant disk group or it can be part of the global hotspare pool for all
disk groups controlled by the controller.
When a physical disk fails, Dell SAS RAID Storage Manager automatically uses
a hotspare to replace it and then rebuilds the data from the failed physical disk
to the hotspare. Hotspares can be used in RAID 1, RAID 5, and RAID 10 storage
configurations.
initialization
The process of writing zeros to the data fields of a virtual disk and, in fault-
tolerant RAID levels, generating the corresponding parity to put the virtual disk
in a Ready state. Initialization erases all previous data on the physical disks. Disk
groups will work without initializing, but they can fail a consistency check
because the parity fields have not been generated.
library
A software component that provides a variety of related functions available to be
used by other software modules.
IO Policy
A virtual disk property indicating whether Cached IO or Direct IO is being used.
In Cached IO mode, all reads are buffered in cache memory. In Direct IO mode,
reads are not buffered in cache memory. Data is transferred to cache and the
host concurrently. If the same data block is read again, it comes from cache
memory. (The IO Policy applies to reads on a specific logical drive. It does not
affect the Read-ahead cache.)
Media Error Count
A physical drive property indicating the number of errors that have been
detected on the disk media.
migration
The process of moving virtual disks and hotspare disks from one controller to
another by disconnecting the physical disks from one controller and attaching
them to another one. The firmware on the new controller will detect and retain
the virtual disk information on the physical disks.