Users guide
Intel® RAID Software User Guide 34
memory that has not been written to disk, the LED signals that this operation needs
to be completed. Upon reboot, the data in memory can then write to the hard disk
drive.
• Although I/O performance may be lower, hard disk drive write-back cache is
disabled by default because data can potentially be lost if a power outage occurs.
Enabling the HDD write-back cache may improve performance, but when enabled,
you should use a UPS (Uninterruptible Power Supply) device to prevent data loss
during power outages.
• Battery life is about three years. You should monitor the battery health and replace
when needed.
• SMART (Self-Monitoring Analysis and Reporting Technology) technology is
supported. This provides a higher level of predictive failure analysis of the hard
disk drives by the RAID controller.
3.5.3 Cache Options and Settings
Cache options and settings can be unique for each virtual drive.
• Cache Write Policy
— Write Through: I/O completion is signaled only after the
data is written to hard
disk.
— Write Back with BBU: I/O completion is signa
led when data is transferred to
cache.
— Always Write Back: Write back is enabled even if
BBU is bad or missing.
• Cache Policy
— Direct I/O: When possible, no cache is involved for
both reads and writes. The
data transfers are directly from host system to the disk and from the disk to the
host system.
— Cached I/O: All reads first look at 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.
• Read Policy
— No Read Ahead: Provides no read ahead for the virtual drive.
— Read Ahead: Reads and buffers additional consecutive stripes/lines
into cache.
— Adaptive: The read ahead automatically turns on and off depending upon
whe
ther the disk is accessed for sequential reads or random reads.
3.5.4 Background Tasks
• Rebuilding a failed drive is performed in the background. The rebuild rate is
tunable from 0-100%.
— The rebuild rate controls the amount of sys
tem resources allocated to the
rebuild.