Areca ARC-1110, ARC-1130, ARC-1231ML/1261ML/1280ML, ARC-1120 Data Protection, Consistency Check

INTRODUCTION

runs as a background task. Auto Reassign Sector discontinues when the operating system makes a request.

1.5.3 Consistency Check

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.

1.6Data Protection

1.6.1BATTERY 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 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.

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