Running 6.2.1, suffered data loss

[mightyball]

I'm running 6 disks, 1 as parity. A couple weeks ago, there was a power outage, and I hadn't put a UPS in yet (I have since). After the system came back, I noticed it was acting a bit odd. After some fiddling trying to figure out what was going on, and a regular reboot cycle, I noticed that one of the disks was marked 'unmountable'. Some googling revealed a corrupted XFS filesystem. xfs_repair did nothing, couldn't find a backup superblock, etc. putting the disk in another system also showed it as corrupt. SMART data for the drive was fine. I tried to 'replace' the drive in unraid, so that it would rebuild it. So i removed it from the array, rebooted, put it back, but it kept seeing it as the old drive and refused to offer the format option. I ended up putting it in another system and repartitioning it. Then Unraid saw it as a new drive, and things proceeded normally. After a day or two of parity rebuild, I checked the drive and... empty.

 

What did I do wrong? Or an i misunderstanding how this is supposed to work?

[JorgeB]

...xfs_repair did nothing, couldn't find a backup superblock, etc.

 

What was the xfs_repair command you used? This error usually happens when it's run on the device, instead of the filesystem.

 

...refused to offer the format option.

 

A disk rebuild wouldn't help a corrupt file system, but for future reference format is never part of a rebuild.

[trurl]

I'm running 6 disks, 1 as parity. A couple weeks ago, there was a power outage, and I hadn't put a UPS in yet (I have since). After the system came back, I noticed it was acting a bit odd. After some fiddling trying to figure out what was going on, and a regular reboot cycle, I noticed that one of the disks was marked 'unmountable'. Some googling revealed a corrupted XFS filesystem. xfs_repair did nothing, couldn't find a backup superblock, etc. putting the disk in another system also showed it as corrupt. SMART data for the drive was fine. I tried to 'replace' the drive in unraid, so that it would rebuild it. So i removed it from the array, rebooted, put it back, but it kept seeing it as the old drive and refused to offer the format option. I ended up putting it in another system and repartitioning it. Then Unraid saw it as a new drive, and things proceeded normally. After a day or two of parity rebuild, I checked the drive and... empty.

 

What did I do wrong? Or an i misunderstanding how this is supposed to work?

Rebuilding from parity will rebuild the disk exactly as it was. This typically means the rebuild will not correct filesystem corruption. And a rebuild of a formatted disk will always result in a formatted disk.

 

The main thing you did wrong was not asking for advice before you did anything.

 

The way you get unRAID to rebuild to the same disk is by starting the array with the disk unassigned so it forgets about the disk assignment, then you can stop, reassign the disk, and start to rebuild.

 

As already mentioned though, rebuild is unlikely to fix filesystem corruption, since filesystem corruption is not a problem with the disk, but a problem with the contents of the disk. And parity typically agrees with the disk contents, so rebuilding will just produce the same contents, which is a corrupt filesystem.

 

Then there was the formatting of the disk. Format means "write an empty filesystem to this disk". That is what it has always meant in every operating system you have ever used. When you format a disk assigned to the parity array, unRAID treats this write of the empty filesytem in exactly the same way it does any other write to a disk, by updating parity. So rebuilding a formatted disk results in a formatted disk.

[JorgeB]

Forgot to add that if you still have the original disk untouched you may still be able to recover most/all data.

[mr-hexen]

What did I do wrong?

 

This:

 

I ended up putting it in another system and repartitioning it.

 

If that was indeed the original disk kiss the data good bye. I highly recommend you come to the forum or contact LT as soon as you're "stuck", not before you start trying this and that.

[ashman70]

Also lets remember that we don't want to be in a situation where we are putting all our eggs in one basket, so to speak. We should have more than one copy of our data. Whilst unRAID offers data protection it is not a backup itself.

[JonathanM]

Whilst unRAID offers data protection

Drive failure protection. Unraid can't recover individual files, only recreate the drive, filesystem errors and all, as a whole.