btrfs send reproducibly fails for a specific subvolume after sending 15 GiB, scrub reports no errors

[Nils Steinger <nst@voidptr.de>]

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Hi,

I recently ran into a problem while trying to back up some of my btrfs
subvolumes over the network:
`btrfs send` works flawlessly on snapshots of most subvolumes, but keeps
failing on snapshots of a certain subvolume — always after sending 15 GiB:

btrfs send /btrfs/snapshots/home/2015-11-17_03:28:14_BOOT-AUTOSNAPSHOT |
pv | ssh kappa "btrfs receive /mnt/300gb/backups/snapshots/zeta/home/"
At subvol /btrfs/snapshots/home/2015-11-17_03:28:14_BOOT-AUTOSNAPSHOT
At subvol 2015-11-17_03:28:14_BOOT-AUTOSNAPSHOT
ERROR: send ioctl failed with -2: No such file or directory
  15GB 0:34:34 [7,41MB/s]

I've tried piping the output to /dev/null instead of ssh and got the
same error (again after sending 15 GiB), so this seems to be on the
sending side.

However, btrfs scrub reports no errors and I don't get any messages in
dmesg when the btrfs send fails.

What could cause this kind of error?
And is there a way to fix it, preferably without recreating the FS?


Regards,
Nils Steinger


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