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RAID Functionality and Features Intel® Integrated RAID Module SROMBSASMR (AXXROMBSASMR) Technical Product Specification
4.3.2 Cache Policies
The RAID cache can temporarily store data so it can be more quickly accessed, or to await
drive readiness. The cache is available both on the RAID controller and hard drives. The RAID
controller read and write cache policy is set on a virtual drive level. This policy is set when the
virtual drive is created, but it can be changed using the Intel
®
RAID BIOS Console 2
configuration utility, the command-line utility, or the Intel
®
RAID Web Console 2 utility.
The user should not enable specific cache policies if the Intel
®
RAID Smart Battery is not
installed. The drive cache is managed through a user-configurable RAID controller option, but
the RAID controller battery does not protect data in the drive cache in the event of a power
interruption. Exercise caution when enabling the 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 are directly from host to disk and from disk to host.
Cache Policy
Cached I/O All reads first look at the cache. If a cache hit occurs, the data is read
from cache; if not, the data is read from disk and the read data is
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 begin 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 receives all the data in a transaction and the data
is successfully written to disk.
Write Policy
Write Back The controller sends a data transfer completion 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.
If the ‘Use Write Through for failed or missing battery’ option is
disabled, the Write Back mode is enabled even if the battery backup
unit is bad or missing.
Hard Drive Cache Read and Write Cache Memory located on the hard drive is used to cache data going to or
coming from the drive. Enabling the hard drive cache can result in a
performance improvement but data held in drive cache is not protected
by the RAID controller.
Revision 1.2
Intel order number E59029-003
22