Re: defragmenting best practice?

[Dave <davestechshop@gmail.com>]

On Thu, Nov 2, 2017 at 7:07 AM, Austin S. Hemmelgarn
<ahferroin7@gmail.com> wrote:
> On 2017-11-01 21:39, Dave wrote:
>> 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?
>>
> The easiest option is to just make sure nobody is logged in and run the
> following shell script fragment:
>
>     for dir in /home/* ; do
>         rm -rf $dir/.cache
>         btrfs subvolume create $dir/.cache
>     done
>
> And then add something to the user creation scripts to create that
> subvolume.  This approach won't pollute /etc/fstab, will still exclude the
> directory from snapshots, and doesn't require any hugely creative work to
> integrate with user creation and deletion.
>
> In general, the contents of the .cache directory are just that, cached data.
> Provided nobody is actively accessing it, it's perfectly safe to just nuke
> the entire directory...

I like this suggestion. Thank you. I had intended to mount the .cache
subvolumes with the NODATACOW option. However, with this approach, I
won't be explicitly mounting the .cache subvolumes. Is it possible to
use "chattr +C $dir/.cache" in that loop even though it is a
subvolume? And, is setting the .cache directory to NODATACOW the right
choice given this scenario? From earlier comments, I believe it is,
but I want to be sure I understood correctly.