Areca ARC-1231ML/1261ML/1280ML User Manual

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runs as a background task. Auto Reassign Sector discontinues 

when the operating system makes a request. 

 

A consistency check is a process that verifies the integrity of 

redundant data. For example, performing a consistency check 

of a mirrored drive assures that the data on both drives of the 

mirrored pair is exactly the same. To verify RAID 3, 5 or 6 redun-

dancy, a consistency check reads all associated data blocks, com-

putes parity, 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.

The SATA 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 RAID controller’s cache, 

thereby permitting any potentially dirty data in the cache to be 

flushed 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-

mal operating conditions, the batteries last for three years before 

replacement is necessary.