DATOptic ARC-1680 Series - Manual (Page 174)

APPENDIX
174
defective. If it is found to have a defect, data will be automatically
relocated, and the defective location is mapped out to prevent
future write attempts.
In the event of an unrecoverable read error, the error will be re-
ported to the host and the location will be flagged as being po-
tentially defective. A subsequent write to that location will initiate
a sector test and relocation should that location prove to have
a defect. Auto Reassign Sector does not affect disk subsystem
performance because it runs as a background task. Auto Reassign
Sector discontinues when the operating system makes a request.
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Consistency Check
A consistency check is a process that verifies the integrity of re-
dundant data. To verify RAID 3, 5, 6, 30, 50 or 60 redundancy, a
consistency check reads all associated data blocks, computes par-
ity, reads parity, and verifies that the computed parity matches
the read parity.
Consistency checks are very important because they detect and
correct parity errors or bad disk blocks in the drive. A consistency
check forces every block on a volume to be read, and any bad
blocks are marked; those blocks are not used again. This is criti-
cal and important because a bad disk block can prevent a disk
rebuild from completing. We strongly recommend that you run
consistency checks on a regular basis—at least once per week.
Note that consistency checks degrade performance, so you should
run them when the system load can tolerate it.
Data Protection
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Battery Backup
The SAS RAID controllers are armed with a Battery Backup Mod-
ule (BBM). While a Uninterruptible Power Supply (UPS) protects
most servers from power fluctuations or failures, a BBM provides
an additional level of protection. In the event of a power failure,
a BBM supplies power to retain data in the SAS RAID controller’s
cache, thereby permitting any potentially dirty data in the cache
to be flushed out to secondary storage when power is restored.