On Mon, 2020-12-21 at 12:48 -0500, Colin Walters wrote:
On Mon, Dec 21, 2020, at 11:28 AM, Ben Cotton wrote:
>
>
> == Summary ==
>
> RPM Copy on Write provides a better experience for Fedora Users as
> it
> reduces the amount of I/O and offsets CPU cost of package
> decompression. RPM Copy on Write uses reflinking capabilities in
> btrfs, which is the default filesystem in Fedora 33.
A bunch of points here:
- No, it's the default for one Edition. Others don't default to
it. And even for Workstation we can't *require* it because it's
definitely supported to use other filesystems and storage layouts.
- Orthogonal to this, I'd also note that xfs supports reflinks too.
Combining those I'd say instead e.g.: "Most Fedora Editions default
to a filesystem that support reflinks, e.g. btrfs or xfs" (actually I
think IoT defaults to ext4 for...probably they didn't consider it?)
Thanks for surfacing this, we'll make the language clearer. About XFS:
it should work, but we haven't tested it extensively, and this work has
been developed primarily with btrfs in mind.
- When talking about RPMs we need to think about container images,
which use overlayfs by default, which defers to the underlying
filesystem for reflinks - so should be fine, but should be explicitly
written down (and tested)
If reflinking isn't possible (which can also happen if e.g. the package
cache and the system are on different filesystems) things work as
normal, albeit with a performance penalty (because more I/O is required
to install the package).
I'll let Matthew weigh in on the other points you raised. Thanks for
the feedback!
Cheers
Davide