Disk redballed - parity OK - disk rebuilds - shows not empty but no data


xusia

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Hi folks, I've searched the forum and haven't found this specific problem. So here goes. Hope you can help.

 

All was well with my array when a drive dropped out showing disabled. It turned out to be the usual culprit - crook SATA cable. Fixed it up, and got the disk showing again. I stopped the array, removed the redball disk. Started the array, stopped the array, added the disk back in. Started the array and data rebuild proceeded as per normal. However, when data rebuild was complete, the disk showed over 1 TB of data in use, but when I accessed the disk to view the files - there was nothing there. Filesystem is xfs - I tried xfs_repair - it looked like it did something, but still no data. Syslog is attached. You may see by the attached syslog that a data rebuild is currently in progress - this is because I repeated the procedure in the hope that the data rebuild would succeed a second time. Anybody got any ideas?

xusia-syslog-20150830-1706.zip

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Hi folks, I've searched the forum and haven't found this specific problem. So here goes. Hope you can help.

 

All was well with my array when a drive dropped out showing disabled. It turned out to be the usual culprit - crook SATA cable. Fixed it up, and got the disk showing again. I stopped the array, removed the redball disk. Started the array, stopped the array, added the disk back in. Started the array and data rebuild proceeded as per normal. However, when data rebuild was complete, the disk showed over 1 TB of data in use, but when I accessed the disk to view the files - there was nothing there. Filesystem is xfs - I tried xfs_repair - it looked like it did something, but still no data. Syslog is attached. You may see by the attached syslog that a data rebuild is currently in progress - this is because I repeated the procedure in the hope that the data rebuild would succeed a second time. Anybody got any ideas?

You say that you tried to access the disk after the xfs_repair - but was this done from the unRAID command line, via the unRAID WebGUI or over the network.  Just asking as xfs_repair may leave files with the wrong permissions for them to be accessed over the network, or it may leave them in the lost+found folder.
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Did you try and stop and start the array after the repair?

 

When I had to run reiserfsck to do a repair years ago - immediately after the repair nothing showed up. But when the drive was re-mounted, all of the files were there.

 

I'll also note that the practice of removing a drive, starting the array, re-installing the same drive, and then doing a rebuild is inherently dangerous. When a cable drops the drive stops being updated, but all of the files that are on the disk at the time is was dropped are still there. Losing a few new files is usually not a huge issue compared to losing the entire disk. When you do a rebuild on top of that disk, you are putting all of your eggs in one basket. It is a far better approach to rebuild onto a different disk. Then, if anything goes wrong with the rebuild, you still have the original disk with all or most of your data as a backup.

 

What I like to do is remove the disk and confirm that the disk is being properly simulated (some call it emulated, same thing). Only if the simulation looks good would I do a rebuild. If someone wants to do a rebuild after confirming the simulation looks good, I consider it a relatively small risk for an experienced user. But it is a risk and they should know that rebuilding onto a different disk is the safer option. For relatively new users, I would recommend the rebuild onto a separate disk. Running a second recovery exercise after a rebuild should only be attempted after a lot of diagnosis and vetting. Because it is so easy to make things worse - and no way to undo.

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Did you try and stop and start the array after the repair?

 

When I had to run reiserfsck to do a repair years ago - immediately after the repair nothing showed up. But when the drive was re-mounted, all of the files were there.

 

I'll also note that the practice of removing a drive, starting the array, re-installing the same drive, and then doing a rebuild is inherently dangerous. When a cable drops the drive stops being updated, but all of the files that are on the disk at the time is was dropped are still there. Losing a few new files is usually not a huge issue compared to losing the entire disk. When you do a rebuild on top of that disk, you are putting all of your eggs in one basket. It is a far better approach to rebuild onto a different disk. Then, if anything goes wrong with the rebuild, you still have the original disk with all or most of your data as a backup.

 

What I like to do is remove the disk and confirm that the disk is being properly simulated (some call it emulated, same thing). Only if the simulation looks good would I do a rebuild. If someone wants to do a rebuild after confirming the simulation looks good, I consider it a relatively small risk for an experienced user. But it is a risk and they should know that rebuilding onto a different disk is the safer option. For relatively new users, I would recommend the rebuild onto a separate disk. Running a second recovery exercise after a rebuild should only be attempted after a lot of diagnosis and vetting. Because it is so easy to make things worse - and no way to undo.

 

Thanks for the info. If I can't get the data back I will remember this for next time. It makes perfect sense and I'm kicking myself for not having done it this way in the first place.

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