Re: defragmenting best practice?

On Wed, Nov 1, 2017 at 8:21 AM, Austin S. Hemmelgarn
[off-list ref] wrote:

quoted

The cache is in a separate location from the profiles, as I'm sure you
know.  The reason I suggested a separate BTRFS subvolume for
$HOME/.cache is that this will prevent the cache files for all
applications (for that user) from being included in the snapshots. We
take frequent snapshots and (afaik) it makes no sense to include cache
in backups or snapshots. The easiest way I know to exclude cache from
BTRFS snapshots is to put it on a separate subvolume. I assumed this
would make several things related to snapshots more efficient too.

Yes, it will, and it will save space long-term as well since $HOME/.cache is
usually the most frequently modified location in $HOME. In addition to not
including this in the snapshots, it may also improve performance.  Each
subvolume is it's own tree, with it's own locking, which means that you can
generally improve parallel access performance by splitting the workload
across multiple subvolumes.  Whether it will actually provide any real
benefit in that respect is heavily dependent on the exact workload however,
but it won't hurt performance.

I'm going to make this change now. What would be a good way to
implement this so that the change applies to the $HOME/.cache of each
user?

The simple way would be to create a new subvolume for each existing
user and mount it at $HOME/.cache in /etc/fstab, hard coding that
mount location for each user. I don't mind doing that as there are
only 4 users to consider. One minor concern is that it adds an
unexpected step to the process of creating a new user. Is there a
better way?