On Fri, Feb 01, 2019 at 11:28:27PM -0500, Alan Hardman wrote:
> I have a Btrfs filesystem using 6 partitionless disks in RAID1 that's failing to mount. I've tried the common recommended safe check options, but I haven't gotten the disk to mount at all, even with -o ro,recovery. If necessary, I can try to use the recovery to another filesystem, but I have around 18 TB of data on the filesystem that won't mount, so I'd like to avoid that if there's some other way of recovering it.
> 
> Versions:
> btrfs-progs v4.19.1
> Linux localhost 4.20.6-arch1-1-ARCH #1 SMP PREEMPT Thu Jan 31 08:22:01 UTC 2019 x86_64 GNU/Linux
> 
> Based on my understanding of how RAID1 works with Btrfs, I would expect a single disk failure to not prevent the volume from mounting entirely, but I'm only seeing one disk with errors according to dmesg output, maybe I'm misinterpreting it:
> 
> [  534.519437] BTRFS warning (device sdd): 'recovery' is deprecated, use 'usebackuproot' instead
> [  534.519441] BTRFS info (device sdd): trying to use backup root at mount time
> [  534.519443] BTRFS info (device sdd): disk space caching is enabled
> [  534.519446] BTRFS info (device sdd): has skinny extents
> [  536.306194] BTRFS info (device sdd): bdev /dev/sdc errs: wr 23038942, rd 22208378, flush 1, corrupt 29486730, gen 2933
> [  556.126928] BTRFS critical (device sdd): corrupt leaf: root=2 block=25540634836992 slot=45, unexpected item end, have 13882 expect 13898

   It's worth noting that 13898-13882 = 16, which is a power of
two. This means that you most likely have a single-bit error in your
metadata. That, plus the checksum not being warned about, would
strongly suggest that you have bad RAM. I would recommend that you
check your RAM first before trying anything else that would write to
your filesystem (including btrfs check --repair).

   Hugo.

> [  556.134767] BTRFS critical (device sdd): corrupt leaf: root=2 block=25540634836992 slot=45, unexpected item end, have 13882 expect 13898
> [  556.150278] BTRFS critical (device sdd): corrupt leaf: root=2 block=25540634836992 slot=45, unexpected item end, have 13882 expect 13898
> [  556.150310] BTRFS error (device sdd): failed to read block groups: -5
> [  556.216418] BTRFS error (device sdd): open_ctree failed
> 
> If helpful, here is some lsblk output:
> 
> NAME   TYPE   SIZE FSTYPE MOUNTPOINT UUID
> sda    disk 111.8G                   
> ├─sda1 part   1.9M                   
> └─sda2 part 111.8G ext4   /          c598dfdf-d6e7-47d3-888a-10f5f53fa338
> sdb    disk   7.3T btrfs             8f26ae2d-84b5-47d7-8f19-64b0ef5a481b
> sdc    disk   7.3T btrfs             8f26ae2d-84b5-47d7-8f19-64b0ef5a481b
> sdd    disk   7.3T btrfs             8f26ae2d-84b5-47d7-8f19-64b0ef5a481b
> sde    disk   7.3T btrfs             8f26ae2d-84b5-47d7-8f19-64b0ef5a481b
> sdf    disk   2.7T btrfs             8f26ae2d-84b5-47d7-8f19-64b0ef5a481b
> sdh    disk   2.7T btrfs             8f26ae2d-84b5-47d7-8f19-64b0ef5a481b
> 
> My main system partition on sda mounts fine and is usable to work with the btrfs filesystem that's having issues.
> 
> Running "btrfs check /dev/sdb" exits with this:
> 
> Opening filesystem to check...
> Incorrect offsets 13898 13882
> ERROR: cannot open file system
> 
> Also, "btrfs restore -Dv /dev/sdb /tmp" outputs some of the files on the filesystem but not all of them. I'm not sure if this is limited to the files on that physical disk, or if there's a bigger issue with the filesystem. I'm not sure what the best approach from here is, so any advice would be great.

-- 
Hugo Mills             | If it's December 1941 in Casablanca, what time is it
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PGP: E2AB1DE4          |                               Rick Blaine, Casablanca