Re: Updating the wiki pages adding btrfs command

[Josh Berry <des@condordes.net>]

On Wed, Sep 15, 2010 at 15:37, Chris Ball <cjb@laptop.org> wrote:
=2E..
> =C2=A0 > Why not just do:
> =C2=A0 > # btrfs subvolume delete /path/to/subvolume1
> =C2=A0 > # btrfs subvolume delete /path/to/subvolume2
> =C2=A0 > # sync
>
> Or even better, "btrfs filesystem sync <path>".
>
> I'm assuming that the caller wants to wait until the subvol delete
> has happened, but is unwilling to wait until all other writes to the
> FS have finished, and is even more unwilling to wait for all writes
> on the rest of the system to finish.
>
> I don't know whether that's actually a reasonable/plausible use case,
> though.

I think so, because I have that use case (sorta).  I have a home
fileserver with btrfs, and a cron job on that machine runs hourly,
taking snapshots.  However, once the disk fills up, I want to delete
the oldest snapshots:

while [[ disk > xx% full ]]; do
    btrfs subvol delete /the/oldest/snapshot
    wait for space to free up
done

If delete does not wait to free space, I'll delete too many snapshots.
 But if I force a filesystem-wide sync after every delete, the loop
may take longer, which on a system busier than mine could take more
than the hour to complete.

-- Josh
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