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Debian Buster: Is it safe to use on autodefrag on a Btrfs filesystem that is used for (Restic) backup only with no Btrfs snapshots or subvolumes?

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Hi All,

First time on the mailing list.

*System:*

OS: Debian Buster with KDE
CPU: Intel Core i3-2100
RAM: 8 GB
OS SSD: 1 TB Crucial MX500 SSD, where /home folder is located. Formatted as
ext4
Other HDD: 2 x 2 TB Toshiba L200 HDD, both used completely for Btrfs RAID1
(files and metadata) with a single subvolume, no Btrfs snapshots

*Goal:*

To store rotating snapshots of some folders in /home/MyUsername/ (located
on SSD) on the Btrfs filesystem located on the 2 HDDs. I've chosen Restic
<https://restic.net/> for this since rsnapshot's developer switched to Borg
and Borg doesn't do snapshots.

*Problem:*

I want to minimize fragmentation on the Btrfs file system, but Debian's
Wiki recommends against usin <https://wiki.debian.org/Btrfs#Recommendations>g
-autodefrag. The reason for this seems to be found in the Warnings section
<https://wiki.debian.org/Btrfs#Warnings>:

>
>    - Mounting with -o autodefrag will often duplicate reflinked or
>    snapshotted files when a balance is run. (TODO: is this still current for
>    linux-4.19.x?)
>    - Any "btrfs filesystem defrag" operation can potentially duplicate
>    reflinked or snapshotted blocks. Files with shared extents lose their
>    shared reflinks, which are then duplicated with n-copies. The effect of the
>    lack of "snapshot aware defrag" is that volumes that make heavy use of
>    reflinks or snapshots will unexpectedly run out of free space. Avoid this
>    by minimizing the use of snapshots, and instead use deduplicating backup
>    software to store backups efficiently (eg: borgbackup).
>
> *Question:*

Given that Restic:

   - doesn't use reflinks
   - uses its own snapshot system (not Btrfs')
   - performs deduplication

Is it safe to use autodefrag for my use case?

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Thread

Debian Buster: Is it safe to use on autodefrag on a Btrfs filesystem  that is used for (Restic) backup only with no Btrfs snapshots or subvolumes? Judah Richardson <judahrichardson@gmail.com> - 2019-07-29 17:30 +0200
  Re: Debian Buster: Is it safe to use on autodefrag on a Btrfs filesystem that is used for (Restic) backup only with no Btrfs snapshots or subvolumes? Stefan Monnier <monnier@iro.umontreal.ca> - 2019-07-29 20:10 +0200
    Re: Debian Buster: Is it safe to use on autodefrag on a Btrfs  filesystem that is used for (Restic) backup only with no Btrfs snapshots or  subvolumes? David Wright <deblis@lionunicorn.co.uk> - 2019-07-29 23:50 +0200
      Re: Debian Buster: Is it safe to use on autodefrag on a Btrfs filesystem that is used for (Restic) backup only with no Btrfs snapshots or subvolumes? Stefan Monnier <monnier@iro.umontreal.ca> - 2019-07-30 00:00 +0200
    Re: Debian Buster: Is it safe to use on autodefrag on a Btrfs filesystem that is used for (Restic) backup only with no Btrfs snapshots or subvolumes? Mart van de Wege <mvdwege@gmail.com> - 2019-07-31 13:00 +0200
      Re: Debian Buster: Is it safe to use on autodefrag on a Btrfs  filesystem that is used for (Restic) backup only with no Btrfs snapshots or subvolumes? Judah Richardson <judahrichardson@gmail.com> - 2019-07-31 16:10 +0200

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