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Also some combinations of devices can create problems. We had a RAID controller that randomly rebuild mirrored sets because the drive was 'dead'. After the rebuild the drive seemed fine. We concluded there was some firmware delay that caused the controller to time out some operation and call the drive 'failed'.

We replaced the drives with a different brand and the 'failures' went away.

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> We concluded there was some firmware delay that caused the controller to time out some operation and call the drive 'failed'.

There is indeed a firmware setting on how long the drive spends checking for errors after it detects one, during which the drive doesn't respond. Sometimes this is too long for the RAID controller, so it drops it.

It used to be you could buy WD Caviar Black drives and tweak that timeout setting on the controller to effectively have WD RE drives (enterprise version of the WD Black drives). They removed that "feature" a few years ago.

Ha! Yes they were WD drives we replaced.

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