Surviving Disk Errors

driveOver the last couple of days, there have been a small but growing number of errors reported on disk one of my NAS (RAID 1, so mirrored). I wasn’t too concerned, as it didn’t look calamitous. I had a spare disk somewhere, I would fix it when I had a moment. Meanwhile the NAS device worked around the errors.

Last night, the RAID simply shut down, and it wouldn’t come up again this morning. I unplugged the faulty drive, and tried starting the NAS with the single good drive, nothing.

This didn’t hold me up, at all, as I keep the same data backed up to yet another drive; so it was just a matter of pointing my mapped drives elsewhere. But at moments during the day, I would try something on the old NAS, and still fail.

Then tonight, I put both disks back in, turned it on, and looked at the error lights that were flashing. I had been wrong, it wasn’t disk one, with the errors, that had failed, but disk two – totally, utterly dead.

I then restarted the NAS with disk one in place, and not disk two, and it all worked, straight out. A very quick copy of the few bits of data that hadn’t made the last backup means that *all* my data is safe. A new drive has replaced disk two, and the NAS is resyncing. Sometime tomorrow, when this is done, I will replace the errored disk one with another new drive, and let that sync from the replaced disk two.

What we learn from this:

  • Always have a backup. If you can have more than one backup, that’s even better.
  • When something goes wrong, look, and look again, before rushing into action. The problem might not be the “obvious” thing you think it is.
  • When you decide a disk needs replacing, replace it then. Don’t think “oh, it will probably be ok for another day or two”.

One Comment

  1. chris
    November 27, 2015

    Disk 2 had successfully synced during the night. Just replaced Disk 1 (which was the one that had the errors, but turned out not to be the one that failed) with a second new drive, and it has begun syncing again. Everything looking good.

    This does mean that I need to get two new drives – as the two I have used were intended to populate the empty NAS drive my friend Tom recently gave me. The ultimate idea is that I will have two identical RAID-1 drives – one in my office, one elsewhere, backing up to each other automatically. These 2TB drives (currently only at 35%) contain everything digital that I have – including personal stuff, ebooks, music and video.

    Separate from that, my personal documents and photographs, stuff that is truly irreplaceable, are incrementally backed up to a separate USB drive hanging off the office NAS, as well as (mostly) being balanced to an encrypted cloud drive.

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