Q&A: Breaking RAID

Q I have a Data Tale 4-Bay RAID system running in 0+1 mode, which is getting filled up with video material that I want to keep. Can I remove its disks to storage and replace them with fresh drives? If so, what disks should I use, and how would I do it?

A This system is made by ONNTO and uses standard drives which you should be able to replace with any compatible 3.5” SATA II hard disk. The manufacturer wisely recommends using identical models from the same manufacturer, although that is not essential.

In RAID 0+1, the disks are set to work as two pairs; within each pair, data is striped for speed of access, then mirrored across the two pairs, to provide resilience against failure or error.

You should be able to remove one striped pair, half the mirror, and the system will then be able to rebuild the mirrored pair from either set of striped disks. You would therefore need to pull either drives 1 and 2, or 3 and 4, when the RAID is shut down. Rebuilds can occur when the system is running but disconnected from a computer, which may be the best answer.

Comments Breaking a RAID mirror to allow the pair to be rebuilt is a standard technique for generating a complete backup with minimum effort.

The principle is very simple: at the end of each working day, pop one of the mirror sets from your RAID system, and replace that drive or those drives with freshly formatted disks. The RAID system will then rebuild the mirror overnight. You take the removed drive(s) home with you. Then if disaster strikes, all you need is another identical RAID system, into which you can place the backup drives. Again the RAID system will rebuild the mirror set, and it is ready to use.

Updated from the original, which was first published in MacUser volume 28 issue 16, 2012.