BTRFS Cache drive: Unmountable: No file system


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Hello all.

 

I am having a problem with my btrfs cache drives on Unraid and I am hoping someone here can help me? I am very much in over my head.

 

I was adding a USB PCI card to my machine and must have loosened the SATA cable on one of my cache drives in the process, because when I restarted Unraid it said the drive was missing. So I powered down, resat the cable, and powered up. When I did so, the cache drive was listed, but as unmounted, not under the cache. I did some searching here and several posts said to just remount the drive, so I did that. Now with the Array started it says "Unmountable: No file system".

 

So, per the FAQ here I ran "mount -o degraded,usebackuproot,ro /dev/sdc1 /x", and it mounted (the first command listed didn't work). But if I look at the /x files it only shows the one cache drive having any files, not the other.

 

Have I lost all my data that had been on that other drive? I honestly can't remember if I had parity set up for the cache-- I did at one point, but the disks are two different sizes and it was causing problems, so I can't remember if I turned off the parity or if I fixed it some other way.

 

I am in the process of copying all the files from /x to a share on the array using the terminal command line. So far several files have had "input/output errors", but nothing I'll miss. Docker.img was one, but I know how to rebuild that. Are those the I/O errored files the only ones that are going to be lost, and the rest should be okay?

 

I'm just not sure what to look for before I reformat the cache drives after copying and want to lose as little as possible.

 

My diagnostics are attached.

mediiia-diagnostics-20210108-1359.zip

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When you re-added the dropped device it was wiped:

Jan  8 12:58:33 MEDiiiA emhttpd: shcmd (210): /sbin/wipefs -a /dev/sdf1
Jan  8 12:58:35 MEDiiiA root: /dev/sdf1: 8 bytes were erased at offset 0x00010040 (btrfs): 5f 42 48 52 66 53 5f 4d

There would have been a warning on the GUI that all data on that device would be deleted, you can try this to recover the superblock with the array stopped:

btrfs-select-super -s 1 /dev/sdf1

 

Then start the array, most likely it will still be unmountable since the other device was re-balanced, but maybe you can then recover at least some data manually using the options in the FAQ.

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14 hours ago, JorgeB said:

When you re-added the dropped device it was wiped:


Jan  8 12:58:33 MEDiiiA emhttpd: shcmd (210): /sbin/wipefs -a /dev/sdf1
Jan  8 12:58:35 MEDiiiA root: /dev/sdf1: 8 bytes were erased at offset 0x00010040 (btrfs): 5f 42 48 52 66 53 5f 4d

There would have been a warning on the GUI that all data on that device would be deleted, you can try this to recover the superblock with the array stopped:


btrfs-select-super -s 1 /dev/sdf1

 

Then start the array, most likely it will still be unmountable since the other device was re-balanced, but maybe you can then recover at least some data manually using the options in the FAQ.

 

Thank you for your response. I was able to recover pretty much everything important-- I used the FAQ here and mounted the cache as read only and when I copied the data over there were a ton of files with I/O errors, but they were almost entirely Plex cache and incomplete downloads (i.e. nothing I would miss). The docker.img was lost but I already knew how to recreate that.

 

So I went ahead and just reformatted and then copied the good files back over.

 

For future reference though, what should I have done in that situation, when the second cache drive became unmounted? Because all of the posts I saw here had said to just remount it, but from what you're saying that's what caused the filesystem to be erased. I just want to be prepared for the future.

 

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11 hours ago, emeybee said:

what should I have done in that situation, when the second cache drive became unmounted?

You can never just re-add the member to the pool, all data will be deleted like mentioned in the warning, if it happens again post diags because the best way is not always the same, it depends on the situation.

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