Areca ARC-1280ML Manual de usuario descargar pdf (Pagina 172)

APPENDIX

172

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 or 6 redundancy, a consistency

check reads all associated data blocks, computes parity, 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 SATA RAID controllers are armed with a Battery Backup Mod-

ule (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.

The batteries in the BBM are recharged continuously through a

trickle-charging process whenever the system power is on. The

batteries protect data in a failed server for up to three or four

days, depending on the size of the memory module. Under nor-

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