Areca 24/4 Internal/External Port Pcie 3.0 12 Gb/s SAS/SATA Raid Controller 2Gb Cache - Manual (Page 252)

APPENDIX
252
rebuild priority to balance volume access and rebuild tasks
appropriately. The Background Task Priority is a relative indi-
cation of how much time the controller devotes to a back
ground operation, such as rebuilding or migrating.
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
require 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 SAS RAID controller 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 media
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 cy-
clic redundancy check (CRC) checksums stored at the end of
each sector.