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Re: BTRFS snapshot space consumption (was: New laptop: need advice on choice...)




On Sat, Apr 13, 2019 at 7:08 PM Felix Miata <mrmazda@xxxxxxxxxxxxx> wrote:
>
> Anders Andersson composed on 2019-04-13 17:31 (UTC+0200):
>
> > Felix Miata wrote:
>
> >> Because of its snapshotting, BTRFS requires considerably more space than older
> >> filesystems, as much as double.
>
> > A btrfs snapshot takes approximately zero space. Where did you get
> > this idea from?
>
> (not an exhaustive list)
>
> 1: "Disk Space Full Because of Snapper" on https://en.opensuse.org/SDB:BTRFS
>
> 2: Since 2015, BTRFS has been the default / filesystem on openSUSE, which
> recommends minimum / filesystem size of 20GB for EXT4, compared to 40GB for BTRFS.
>
> 3: Much more common / filesystem freespace exhausted threads on mailing lists and
> web forums from BTRFS users compared to EXT4 users, with the usual recommendation
> to delete one or more snapshots to free space.
>
> 4: https://btrfs.wiki.kernel.org/index.php/FAQ#Help.21_I_ran_out_of_disk_space.21
>
> 5: https://btrfs.wiki.kernel.org/index.php/FAQ#Why_is_free_space_so_complicated.3F
>
> 6:
> https://www.linuxquestions.org/questions/linux-containers-122/docker-on-btrfs-using-much-space-in-var-lib-docker-btrfs-4175622037/#post5811463



Of course you will run out of space if you keep taking snapshots!
Btrfs never does this, but you can do it *manually* or with
third-party tools. When you take a snapshot, btrfs will keep
everything until it's deleted. That's why everyone says that if you
run out of space, you can delete snapshots. If the advise to the user
is to delete a snapshot, it is something that the user did *because*
they wanted to retain those files.

The "Snapper" user has *installed* a tool that takes snapshots all the
time - obviously you will run out of space because every file you
modify or delete will still be stored in its original version until
you remove the snapshot.