Re: BTRFS raid6 unmountable after a couple of days of usage.

[Austin S Hemmelgarn]

On 2015-07-14 07:49, Austin S Hemmelgarn wrote:

So, after experiencing this same issue multiple times (on almost a dozen 
different kernel versions since 4.0) and ruling out the possibility of it being 
caused by my hardware (or at least, the RAM, SATA controller and disk drives 
themselves), I've decided to report it here.

The general symptom is that raid6 profile filesystems that I have are working 
fine for multiple weeks, until I either reboot or otherwise try to remount 
them, at which point the system refuses to mount them.

I'm currently using btrfs-progs v4.1 with kernel 4.1.2, although I've been 
seeing this with versions of both since 4.0.

Output of 'btrfs fi show' for the most recent fs that I had this issue with:
         Label: 'altroot'  uuid: 86eef6b9-febe-4350-a316-4cb00c40bbc5
        Total devices 4 FS bytes used 9.70GiB
        devid    1 size 24.00GiB used 6.03GiB path /dev/mapper/vg-altroot.0
        devid    2 size 24.00GiB used 6.01GiB path /dev/mapper/vg-altroot.1
        devid    3 size 24.00GiB used 6.01GiB path /dev/mapper/vg-altroot.2
        devid    4 size 24.00GiB used 6.01GiB path /dev/mapper/vg-altroot.3

         btrfs-progs v4.1

Each of the individual LVS that are in the FS is just a flat chunk of space on 
a separate disk from the others.

The FS itself passes btrfs check just fine (no reported errors, exit value of 
0), but the kernel refuses to mount it with the message 'open_ctree failed'.

I've run btrfs chunk recover and attached the output from that.

Here's a link to an image from 'btrfs image -c9 -w': 
https://www.dropbox.com/s/pl7gs305ej65u9q/altroot.btrfs.img?dl=0
(That link will expire in 30 days, let me know if you need access to it beyond 
that).

The filesystems in question all see relatively light but consistent usage as 
targets for receiving daily incremental snapshots for on-system backups (and 
because I know someone will mention it, yes, I do have other backups of the 
data, these are just my online backups).

Further updates, I just tried mounting the filesystem from the image above again, this time passing device= options for each device in the FS, and it seems to be working fine now. I've tried this with the other filesystems however, and they still won't mount.

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