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I wanted to test performance in a RAID10 with a "damaged drive". To simulate this situation I've set a single drive to "Offline" by using this command:

MegaCli -PDOffline -PhysDrv [45:12] -aAll

The drive went offline but directly with this command another drive switched to "failed". I checked the status of all drives before performing this command. All were marked as online.

Does setting a drive "offline" puts a lot of pressure on the hardware so the risk of damaging a disk increases heavily? Is this behaviour common?

I'm using MegaRAID SAS 9280-4i4e and SATA drives.

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2 Answers 2

up vote 3 down vote accepted

No, there's no such thing as "pressure" on hardware that causes damage. Likely what happened is that the MegaRAID software wasn't designed to handle a drive being switched off line by command while it was a functional part of a RAID array.

I doubt the disk is actually damaged. More likely the controller just thought it was. If the drive actually is damaged, it's most likely coincidence. (I'm not sure I'd be confident enough in that diagnosis that I'd be willing to try it again though.)

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A bug in MegaCli would indeed be way more likely. The drives are less than one week old. How are the chances that a single drive would fail within a given ~20 second timespan? Close to impossible.. I've reported this to LSI. –  Philip Mar 22 '12 at 21:07

As far as I know normally when a raid becomes degraded there will only be extra load on the drives when it is rebuilding. A rebuild may happen automatically if there is a hot spare, otherwise you need to start it yourself or it will start once a replacement or spare has been added.

As long as there is no rebuild happening there shouldn't be an extra load.

A raid10 will only have a limited increase in load during a rebuild and only for the drive that was a mirror of the bad drive.

A raid5 will see a very large performance penalty during a rebuild, because all drives are involved in the rebuild process.

Your action in and of itself should not have caused any problems (except degrading the raid). I am suspecting you are the victim of a bug. A better way, in my opinion, to test raid redundancy is to just take out the drive. Not a scenario that's all too uncommon. ;-)

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