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Write-Back Cache
Write-Back cache refers to a caching strategy whereby write operations result in a
completion status being sent to the host operating system as soon as the cache
(not the disk drive) receives the write data. The target drive receives the data at a
more appropriate time in order to increase controller performance.
In a dual-active configuration, write data is always copied to the cache of the
second controller before completion status is issued to the host initiator.
Write-Back cache mode is not recommended due to potential data loss in
NOTE:
the event of a power outage.
RAID Management
RAID is an acronym for Redundant Array of Independent Disks. The Ultra S2S
RAID Controller implements several different versions of the RAID technology
and two special versions that are specific to this controller. Each version is
referred to as a RAID level.
An appropriate RAID level is selected when the logical units are defined or
created.
Supported RAID Levels
The Ultra S2S RAID Controller supports RAID levels 0, 1, 3, 0+1, 5, and JBOD.
Drives within an individual subsystem can use different RAID levels and a single
drive within the system can be configured to use more than one RAID level.
Striping (RAID 0)
Striping refers to the storing of a sequential block of incoming data across
multiple drives in a drive group. For example, if there are three drives in a drive
group (or pack), the data is separated into blocks. A block of data can be specified
to be either 16, 32, 64, or 128 sectors in depth. Block one of the data will be stored
on drive one, block two on drive two, block three on drive three. Drive one will
again be the location of the next block (block four); then block five is stored on
drive two, block six on drive three, and so forth. This method can significantly
increase disk system throughput, particularly for transferring large, sequential
data blocks.
Introduction
13
RAID Management
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