bug#51787: Disk performance on ci.guix.gnu.org

[Mathieu Othacehe <othacehe@gnu.org>]

Hello Ricardo,

> Should we attempt to overwrite /gnu/store and rely exclusively on
> substitutes from the cache?

Yes, I don't see any other options. Before that, what might be nice
could be:

1. Ensure that all Berlin /var/cache/guix/publish directory is
synchronized on Bordeaux. We are now at 117G out of X. We could then
start a publish server on Bordeaux. As Bordeaux is already part of the
default substitute servers list, the transition could be smooth I guess.

2. Determine what file-system out of ext4, btrfs and xfs could be the
most suitable for Berlin's /gnu/store. I'm running some tests on an old
HDD to try to determine the fragmentation impact on those
file-systems. We can of course choose to be conservative and go for ext4
that did the job until now.

Regarding the /gnu/store re-creation, I wonder how can we do it without
reinstalling completely Berlin. Maybe we could save the system store
closure somewhere and restore it on the shining new file-system?

Thanks,

Mathieu