using snapshot for backup: best practise?

using snapshot for backup: best practise?

[Ulli Horlacher]

I am using fsfreeze when running a backup to ensure a consistent filesystem.

While the backup is running writes to the filesystem are suspended and the
whole system is unresponsive, e.g. logins are not possible.
On certain errors the unfreeze will not happen and the system is locked
forever.

Using snapshots seems a better idea for backups :-)

But snapshots do not include subvolumes.

For example the / filesystem has the subvolumes:
/home
/home/tux/test
/var/spool

When I run the command:

btrfs subvolume snapshot / /.snapshot/_

the snapshot will contain only the root subvolume.

I have to manually add:

rmdir /.snapshot/_/home
btrfs subvolume snapshot /home /.snapshot/_/home
rmdir /.snapshot/_/home/tux/test
btrfs subvolume snapshot /home/tux/test /.snapshot/_/home/tux/test
rmdir /.snapshot/_/var/spool
btrfs subvolume snapshot /var/spool /.snapshot/_/var/spool

Then run the backup on /.snapshot/_ und afterwards:

btrfs subvolume del /.snapshot/_/var/spool
btrfs subvolume del /.snapshot/_/home/tux/test
btrfs subvolume del /.snapshot/_/home
btrfs subvolume del /.snapshot/_

But this will work only for this special example!
And I have hundreds of systems to backup with different filesystem layout!

Is there a best practise "Using snapshots for making backup"?
I need automatic detecting, creating and removing of nested snapshots.

-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    https://www.tik.uni-stuttgart.de/
REF:<20250626114345.GA615977@tik.uni-stuttgart.de>

Re: using snapshot for backup: best practise?

[Graham Cobb]

I do various sorts of backups but the main one built around snapshots 
uses btrbk. It doesn't solve the problem you mention below but it does 
reduce the problem to listing each subvolume once in the config file 
(which can easily be automated if you want). For example, here is an 
extract from the btrbk.conf on one of my systems:

#
# Data pool
#
volume /mnt/data
  snapshot_dir btrbk_snapshots
  snapshot_create onchange
  preserve_day_of_week monday

# On the disk itself only keep recent snapshots
  snapshot_preserve_min  5d
  snapshot_preserve 10d 4w
  timestamp_format long-iso

# On the backup disk keep historic monthlies
  target_preserve_min no
  target_preserve 30d 8w *m
  target send-receive    /snapshots/black_snapshots

#Do not snapshot the deb-proxy cache
#subvolume home/cache
# Do not snapshot emergency
#subvolume emergency
subvolume home/boinc-client
# For boinc just keep the latest plus one daily
  snapshot_preserve_min latest
  snapshot_preserve 1d
  target_preserve 4d 1w 1m
subvolume home/cobb
subvolume home/default-user
subvolume home/dmarc-staging
subvolume home/imap-archive
subvolume projects
subvolume home/mywiki
.
.
.

And, of course, btrbk handles all the management of the snapshots 
themselves (see the first half of the example file above, which keeps 10 
daily snapshots and 4 weekly snapshots on the disk itself and a 
different selection on another disk).


On 26/06/2025 12:43, Ulli Horlacher wrote:
> 
> I am using fsfreeze when running a backup to ensure a consistent filesystem.
> 
> While the backup is running writes to the filesystem are suspended and the
> whole system is unresponsive, e.g. logins are not possible.
> On certain errors the unfreeze will not happen and the system is locked
> forever.
> 
> Using snapshots seems a better idea for backups :-)
> 
> But snapshots do not include subvolumes.
> 
> For example the / filesystem has the subvolumes:
> /home
> /home/tux/test
> /var/spool
> 
> When I run the command:
> 
> btrfs subvolume snapshot / /.snapshot/_
> 
> the snapshot will contain only the root subvolume.
> 
> I have to manually add:
> 
> rmdir /.snapshot/_/home
> btrfs subvolume snapshot /home /.snapshot/_/home
> rmdir /.snapshot/_/home/tux/test
> btrfs subvolume snapshot /home/tux/test /.snapshot/_/home/tux/test
> rmdir /.snapshot/_/var/spool
> btrfs subvolume snapshot /var/spool /.snapshot/_/var/spool
> 
> Then run the backup on /.snapshot/_ und afterwards:
> 
> btrfs subvolume del /.snapshot/_/var/spool
> btrfs subvolume del /.snapshot/_/home/tux/test
> btrfs subvolume del /.snapshot/_/home
> btrfs subvolume del /.snapshot/_
> 
> But this will work only for this special example!
> And I have hundreds of systems to backup with different filesystem layout!
> 
> Is there a best practise "Using snapshots for making backup"?
> I need automatic detecting, creating and removing of nested snapshots.
> 

Re: using snapshot for backup: best practise?

[Ulli Horlacher]

On Thu 2025-06-26 (13:41), Graham Cobb wrote:

> I do various sorts of backups but the main one built around snapshots
> uses btrbk. It doesn't solve the problem you mention below but it does
> reduce the problem to listing each subvolume once in the config file

btrbk does some sort of snapshot rotation?

For this I have already a perfect solution:

https://fex.belwue.de/linuxtools/snaprotate.html

But snapshots are not a backup.


-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    https://www.tik.uni-stuttgart.de/
REF:<f36e47c9-f135-473c-b1f1-2fedaef8aa10@cobb.uk.net>

Re: using snapshot for backup: best practise?

[Ulli Horlacher]

On Thu 2025-06-26 (13:43), Ulli Horlacher wrote:

> Using snapshots seems a better idea for backups :-)
> 
> But snapshots do not include subvolumes.
> 
> When I run the command:
> 
> btrfs subvolume snapshot / /.snapshot/_
> 
> the snapshot will contain only the root subvolume.

Mewanwhile I have written some (more) tools to handle nested subvolumes
and snapshots.

Example:

root@fex:~# btrfs_list /local/test
ACCESS-MODE SUBVOLUME <- SNAPSHOT-PARENT
rw /local/test
rw /local/test/sv1
rw /local/test/sv1/sv1_1
rw /local/test/sv1/sv1_1/ss <- /local/test/sv1/sv1_1
rw /local/test/sv1/sv1_2
rw /local/test/sv2

root@fex:~# btrfs_rsnapshot /local/test
Create a snapshot of '/local/test' in '/local/test/.snapshot/test'
Create a snapshot of '/local/test/sv1' in '/local/test/.snapshot/test/sv1'
Create a snapshot of '/local/test/sv1/sv1_1' in '/local/test/.snapshot/test/sv1/sv1_1'
Create a snapshot of '/local/test/sv1/sv1_1/ss' in '/local/test/.snapshot/test/sv1/sv1_1/ss'
Create a snapshot of '/local/test/sv1/sv1_2' in '/local/test/.snapshot/test/sv1/sv1_2'
Create a snapshot of '/local/test/sv2' in '/local/test/.snapshot/test/sv2'

root@fex:~# btrfs_list /local/test
ACCESS-MODE SUBVOLUME <- SNAPSHOT-PARENT
rw /local/test
ro /local/test/.snapshot/test <- /local/test
ro /local/test/.snapshot/test/sv1 <- /local/test/sv1
ro /local/test/.snapshot/test/sv1/sv1_1 <- /local/test/sv1/sv1_1
ro /local/test/.snapshot/test/sv1/sv1_1/ss <- /local/test/sv1/sv1_1/ss
ro /local/test/.snapshot/test/sv1/sv1_2 <- /local/test/sv1/sv1_2
ro /local/test/.snapshot/test/sv2 <- /local/test/sv2
rw /local/test/sv1
rw /local/test/sv1/sv1_1
rw /local/test/sv1/sv1_1/ss <- /local/test/sv1/sv1_1
rw /local/test/sv1/sv1_2
rw /local/test/sv2

root@fex:~# btrfs_rsnapshot -d /local/test
Delete subvolume (no-commit): '/local/test/.snapshot/test/sv2'
Delete subvolume (no-commit): '/local/test/.snapshot/test/sv1/sv1_2'
Delete subvolume (no-commit): '/local/test/.snapshot/test/sv1/sv1_1/ss'
Delete subvolume (no-commit): '/local/test/.snapshot/test/sv1/sv1_1'
Delete subvolume (no-commit): '/local/test/.snapshot/test/sv1'
Delete subvolume (no-commit): '/local/test/.snapshot/test'

root@fex:~# btrfs_list /local/test
ACCESS-MODE SUBVOLUME <- SNAPSHOT-PARENT
rw /local/test
rw /local/test/sv1
rw /local/test/sv1/sv1_1
rw /local/test/sv1/sv1_1/ss <- /local/test/sv1/sv1_1
rw /local/test/sv1/sv1_2
rw /local/test/sv2


-- 
Ullrich Horlacher              Server und Virtualisierung
Rechenzentrum TIK
Universitaet Stuttgart         E-Mail: horlacher@tik.uni-stuttgart.de
Allmandring 30a                Tel:    ++49-711-68565868
70569 Stuttgart (Germany)      WWW:    https://www.tik.uni-stuttgart.de/
REF:<20250626114345.GA615977@tik.uni-stuttgart.de>

Re: using snapshot for backup: best practise?

[Mark Harmstone]

On 26/06/2025 12.43 pm, Ulli Horlacher wrote:
> 
> I am using fsfreeze when running a backup to ensure a consistent filesystem.
> 
> While the backup is running writes to the filesystem are suspended and the
> whole system is unresponsive, e.g. logins are not possible.
> On certain errors the unfreeze will not happen and the system is locked
> forever.
> 
> Using snapshots seems a better idea for backups :-)
> 
> But snapshots do not include subvolumes.

Omar Sandoval had patches to add recursive snapshotting to btrfs-progs, but
they never made it in, for reasons I can't remember.

> For example the / filesystem has the subvolumes:
> /home
> /home/tux/test
> /var/spool
> 
> When I run the command:
> 
> btrfs subvolume snapshot / /.snapshot/_
> 
> the snapshot will contain only the root subvolume.
> 
> I have to manually add:
> 
> rmdir /.snapshot/_/home
> btrfs subvolume snapshot /home /.snapshot/_/home
> rmdir /.snapshot/_/home/tux/test
> btrfs subvolume snapshot /home/tux/test /.snapshot/_/home/tux/test
> rmdir /.snapshot/_/var/spool
> btrfs subvolume snapshot /var/spool /.snapshot/_/var/spool
> 
> Then run the backup on /.snapshot/_ und afterwards:
> 
> btrfs subvolume del /.snapshot/_/var/spool
> btrfs subvolume del /.snapshot/_/home/tux/test
> btrfs subvolume del /.snapshot/_/home
> btrfs subvolume del /.snapshot/_
> 
> But this will work only for this special example!
> And I have hundreds of systems to backup with different filesystem layout!
> 
> Is there a best practise "Using snapshots for making backup"?
> I need automatic detecting, creating and removing of nested snapshots.
>