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APPENDIX
RAID controller allows user to choose the task priority (Ultra
Low (5%), Low (20%), Medium (50%), High (80%)) to bal
-
ance volume set access and background tasks appropriately.
For high array performance, specify an Ultra Low value. Like
volume initialization, after a volume rebuilds, it does not re
-
quire a system reboot.
High Reliability
•
Hard Drive Failure Prediction
In an effort to help users avoid data loss, disk manufacturers
are now incorporating logic into their drives that acts as an
"early warning system" for pending drive problems. This
system is called SMART. The disk integrated controller works
with multiple sensors to monitor various aspects of the drive's
performance, determines from this information if the drive
is behaving normally or not, and makes available status
information to RAID storage
firmware that probes the drive
and look at it.
The SMART can often predict a problem before failure occurs.
The controllers will recognize a SMART error code and notify
the administer of an impending hard drive failure.
•
Auto Reassign Sector
Under normal operation, even initially defect-free drive me-
dia can develop defects. This is a common phenomenon. The
bit density and rotational speed of disks is increasing every
year, and so are the potential of problems. Usually a drive can
internally remap bad sectors without external help using cyclic
redundancy check (CRC) checksums stored at the end of each
sector.
The RAID controller drives perform automatic defect re-as-
signment for both read and write errors. Writes are always
completed - if a location to be written is found to be defective,
the drive will automatically relocate that write command to a
new location and map out the defective location. If there is
