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I've been using btrfs since 2012, and while as of 2014, it's far from done, it's gone a long way in that time. I thought I'd post some tips and scripts from things I've learned through my own use and sharing with others, hence this page.
More generally, you'll find Btrfs documentation on the btrfs wiki.

Table of Content for btrfs:

More pages: March 2014 April 2014 May 2014 October 2014 March 2018



2018/03/09 Btrfs Tips: Rescuing A Btrfs Send Receive Relationship
π 2018-03-09 01:01 in Btrfs, Linux
I had a problem when migrating disks and moving read only btrfs receive snapshots. I did a
btrfs snapshot dir1/Video_ro.20180220_21:03:41 dir2/Video_ro.20180220_21:03:41 
which in turn broke the snapshot by making it read-write and losing the btrfs receive relationship (Received UUID)

Later, I wanted to re-establish the btrfs send/receive relationship since it was an 8TB subvolume, and I wanted to avoid having to copy back all the data I already had there. Simply making the destination snapshot read only again did not work

The solution was python-btrfs, and this code: https://github.com/knorrie/python-btrfs/commit/1ace623f95300ecf581b1182780fd6432a46b24d

gargamel:python-btrfs/examples# ./set_received_uuid.py 2afc7a5e-107f-d54b-8929-197b80b70828 31337 1234.5678 /mnt/btrfs_bigbackup/DS1/Video_ro.20180220_21:03:411G Current subvolume information: subvol_id: 94887 received_uuid: 00000000-0000-0000-0000-000000000000 stime: 0.0 (1970-01-01T00:00:00) stransid: 0 rtime: 0.0 (1970-01-01T00:00:00) rtransid: 0

Setting received subvolume...

Resulting subvolume information: subvol_id: 94887 received_uuid: 2afc7a5e-107f-d54b-8929-197b80b70828 stime: 1234.5678 (1970-01-01T00:20:34.567800) stransid: 31337 rtime: 1520488877.415709329 (2018-03-08T06:01:17.415709) rtransid: 255755

Then make it read-only again: gargamel:python-btrfs/examples# btrfs property set -ts /mnt/btrfs_bigbackup/DS1/Video_ro.20180220_21:03:41 ro true

But this didn't work: ABORT: btrfs send -p /mnt/btrfs_pool1/Video_ro.20180220_21:03:41 Video_ro.20180308_07:50:06 | btrfs receive /mnt/btrfs_bigbackup/DS1//. failed At subvol Video_ro.20180308_07:50:06 At snapshot Video_ro.20180308_07:50:06 ERROR: cannot find parent subvolume

You can see that with set_received_uuid.py, I set Received UUID to match UUID on the source:

gargamel:/mnt/btrfs_pool1# btrfs subvolume show /mnt/btrfs_bigbackup/DS1/Video_ro.20180220_21:03:41 DS1/Video_ro.20180220_21:03:41
        Name:                   Video_ro.20180220_21:03:41
        UUID:                   cb4f343c-5e79-7f49-adf0-7ce0b29f23b3
        Parent UUID:            0e220a4f-6426-4745-8399-0da0084f8b23 
        Received UUID:          2afc7a5e-107f-d54b-8929-197b80b70828 << changed this
        Creation time:          2018-02-20 21:13:36 -0800
        Subvolume ID:           94887
        Generation:             250689
        Gen at creation:        250689
        Parent ID:              89160
        Top level ID:           89160
        Flags:                  readonly
        Snapshot(s):

Name: Video_ro.20180220_21:03:41 UUID: 2afc7a5e-107f-d54b-8929-197b80b70828 Parent UUID: e5ec5c1e-6b49-084e-8820-5a8cfaa1b089 Received UUID: 0e220a4f-6426-4745-8399-0da0084f8b23 Creation time: 2018-02-20 21:03:42 -0800 Subvolume ID: 11228 Generation: 4174 Gen at creation: 4150 Parent ID: 5 Top level ID: 5 Flags: readonly

Turns out however that because the source had a Parent UUID value too, I was actually supposed to set Received UUID on the destination to it:

gargamel:python-btrfs/examples# ./set_received_uuid.py 0e220a4f-6426-4745-8399-0da0084f8b23 313 37 1234.5678 /mnt/btrfs_bigbackup/DS1/Video_ro.20180220_21:03:41 Current subvolume information: subvol_id: 94887 received_uuid: 2afc7a5e-107f-d54b-8929-197b80b70828 stime: 1234.5678 (1970-01-01T00:20:34.567800) stransid: 31337 rtime: 1520488877.415709329 (2018-03-08T06:01:17.415709) rtransid: 255755

Setting received subvolume...

Resulting subvolume information: subvol_id: 94887 received_uuid: 0e220a4f-6426-4745-8399-0da0084f8b23 stime: 1234.5678 (1970-01-01T00:20:34.567800) stransid: 31337 rtime: 1520537034.890253770 (2018-03-08T19:23:54.890254) rtransid: 256119

gargamel:python-btrfs/examples# btrfs property set -ts /mnt/btrfs_bigbackup/DS1/Video_ro.201802 20_21:03:41 ro true

After this, I was able to re-start my btrfs send/receive and /mnt/btrfs_bigbackup/DS1/Video_ro.201802 20_21:03:41 was properly accepted as a destination. Yeah!


More pages: March 2014 April 2014 May 2014 October 2014 March 2018