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I’ve just finished a weekend-long battle with Apple’s RAID software. In the end, it saved my bacon. But the story is longer than that and holds a couple of warnings about backup strategies. First some background.

I have a old PowerBook running OS X Server that plays the role of media server. It had 3 TB of drive space connected to it. 1 TB was set aside as a network-shared Time Machine back-up drive and the other 2 TB were in a mirrored RAID array. Because movie files, audio, photos, ebooks, etc. take up a lot of space, the decision was made to keep them on a RAID, rather than trying to keep them backed up with Time Machine or some sort of removable media.

Somewhere along the way, one of the two drives in the RAID array failed, and here comes the problem. Apple’s OS X Server product and their software-based RAID software give you no alarm or warning that a RAID array is degraded or failing. The only way I noticed the problem was because movies weren’t streaming properly off the server and I had to use the Disk Utility app to see why one drive wasn’t mounting.

It was at that point that I happened to click on the RAID tab and noticed a big red warning and the word “degraded” next to the RAID volume. Had I not bothered to investigate, it is entirely possible that the second drive in the RAID array could have failed or been corrupted by the first, completely defeating the purpose of the RAID in the first place.

So a few lessons learned:

1. Don’t put cheesy, low-end Western Digital hard drives in a RAID array. You’ll just end up having to constantly rebuild the array.

2. Don’t trust OS X Server to give you any sort of warning about your failing RAID array. Check early and often using Disk Utility.

3. Regardless of 1 and 2, a RAID array is a great way to avoid more expensive or time consuming back-up options like Time Machine or tons of removable media.

p.s. This is partially an exercise in trying out the WordPress -> Twitter functionality. Apologies if anyone finds this post boring.

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