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RAID5 Question

I suspect I'm not going to like the answer to this question, but here goes...

My RAID5 array was "degraded" earlier today and spent a long time "rebuilding".

It seems happy now, but I'm worried.

Does this mean that there was a problem, which the RAID controller sorted out for me automatically ? Or, more worryingly, is this a symptom of an impending catastrophic failure ?

Any hints here would be appreciated.

Steve Jones (UK)
Monday, February 2, 2004

When a disk in a RAID5 array dies, is is considered "degraded", because while your data is still okay, there is no more "R" in your "AID".  The fact that it rebuilt itself imples that the RAID was configured with a hot-standy disk:  A disk that sits there and does nothing until the RAID degrades.

In other words, your RAID just paid off.

So get in there, and replace the disk that died!

Monday, February 2, 2004

Thanks for that. The controller seems happy with all the drives, as far as I can see from the config utility. So, I don't know which drive to replace.

Also, I did a full array "scan with fix" task and it found seven errors, but fixed them. Now I'm confused.

For info, its a three drive RAID5 on a Dell/Adaptec PERC 320 dual channel controller.

Steve Jones (UK)
Tuesday, February 3, 2004

Most of today's drives support SMART which allows you check the drives health through a software utility.  It will actually tell you how much a drive has degraded.

There are several software applications on the market which support this. I use speedfan myself to check my drives from time to time. But most of the time the driver manufacturer also have some tools on their websites.

Jan Derk
Tuesday, February 3, 2004

Dell has an HD scan tool. Run it on the disks and if they come up as failed, you can call support and get a replacement under your support contract.

Tuesday, February 3, 2004

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