Tony Rogers asked:
I have a linux based software RAID 5 array. SMART has just started to send me emails complaining that one of the 5 disks has a Current Pending Sector Count of 9 and also an Offline Uncorrectable Count of 9. I have done a lot of google-ing and the consensus seems to be that if I write the sectors with zeros, the disk will remap them and all will be well.
I did want to track down which files were affected, but I have difficulty doing the mapping as I have 5 disks in RAID 5 with LUKS encryption on top, and finally LVM on top of that. None of the research I did helped me get through that tangle.
In the end, my plan was to simply fail the drive and re-add it to make the array re-build.
Before I did that, I did ‘long’ tests on the other disk in the array. All were perfect apart from one which had a Reallocated Sector count of 82,82,36,764.
So 2 out of 5 drives have issues.
At this point I am a little confused as to the best approach to trying to flush these errors out, if it is at all possible.
Does anyone have any advice? I am happy to replace failing drives where necessary, but would like to try to get the data straight first.
My answer:
This will be the general process. See the mdraid man page and your own local configuration for the exact commands to use, if you don’t already know them.
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Pray.
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Verify that your backup is current. Run it manually if necessary. If you don’t have backups, make one now.
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Fail the drive with pending sector and offline uncorrectable sectors. The other drive with reallocated sectors will live a little longer, and hopefully long enough to complete this process, but this drive is at the point where it could kill your entire array.
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Replace the drive. In hardware. Partition the new drive and add it to the mdraid array.
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Rebuild the array and wait for the rebuild to complete. In newer versions of mdraid, the rebuild will start automatically.
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Repeat the process with the second drive.
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