Areca ARC-1213-4I Bedienungsanleitung PDF herunterladen (Seite 189)

189

APPENDIX

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 agged 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.

• Consistency Check

A consistency check is a process that veries 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 veries 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

• Battery Backup

The RAID controllers are armed with a Battery Backup Module

(BBM). While a Uninterruptible Power Supply (UPS) protects most

servers from power uctuations 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 RAID controller’s cache,

thereby permitting any potentially dirty data in the cache to be

ushed out to secondary storage when power is restored.

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Areca ARC-1213-4I Bedienungsanleitung Seite 189