Technical Product Specification

RAID Functionality and Features Intel® RAID Controller SRCSAS18E
Revision 1.01
Intel order number D61769-001
22
It may be unwise to enable some cache policies if a battery is not installed on the RAID
controller. Drive cache is managed through a user configurable RAID controller option.
However, the RAID controller battery does not protect data in drive cache in the event of a
power interruption. Caution should be exercized in enabling drive cache.
Table 13. Cache Policies
Array Cache
Policy
Cache Option Description
Direct I/O When possible, no cache is involved for both reads and writes. The
data transfers will be directly from host to disk and from disk to host.
Cache Policy
Cached I/O All reads will first look at cache. If a cache hit occurs, the data will be
read from cache; if not, the data will be read from disk and the read
data will be buffered into cache. All writes to drive are also written to
cache.
No Read Ahead The controller does not use read-ahead.
Read Ahead Specifies that additional consecutive data stripes are read and
buffered into cache.
Read Policy
Adaptive Read Ahead Specifies that the controller beins using read ahead if the two most
recent disk accesses occurred in sequential sectors.
Write Through The controller sends a data transfer completion signal to the host after
the disk subsystem recieves all the data in a transaction and the data
is successfully written to disk.
Write Policy
Write Back The controller sends a data transfer completions signal to the host
when the controller cache receives all the data in a transaction and the
data is then written to disk as the drive becomes available.
Hard Drive Cache Read and Write Cache Memory located on the hard disk drive is use to cache data going to or
coming from the drive. Enabling hard drive cache can result in a
performance improvement but data held in drive cache is not protected
by the RAID controller.
4.3.3 Stipe Size
Stripe size determines the size of each data stripe on each hard disk drive. The options are 4, 8,
16, 32, 64, and 128 KB. The stripe size option is set during the virtual drive creation and cannot
be changed without removing the virtual drive configuration and all data contained on the virtual
drive.
4.3.4 Hot Spare Drives
Hot spare drives are drives designated to automatically replace a failed drive. Hot spare drives
must be the same size or larger than the drives they may replace. They can be designated as a
private hot spare drive assigned to one virtual drive, or they may be a global hot spare that is
assigned to all virtual drives attached to the RAID controller. Hot spare drives can be
designated using the Intel
®
RAID BIOS Console 2 utility, the Intel
®
RAID Web Console 2 utility,
or the Command Line utility.