Moving /gnu/store safely?

[Phil <phil@beadling.co.uk>]

Hi all,

My growing /gnu/store needed to be moved to another location.  I couldn't
find any specific instructions on doing this but think I've managed to
cobble together a way of doing this safely without breaking store properties.

There were some gremlins tho - on restarting Guix the /gnu/store was
seen to grow to approximately double it's size.

I seem to have tamed this with the garbage collection, but would be interested
in people's thoughts if this is a reasonable way to do this, or if you
have any hints or gotchas I may have missed?

Stop all Guix services and mounts
    systemctl stop guix-daemon.service
    systemctl stop gnu-store.mount
    systemctl status guix-daemon.service
    systemctl status gnu-store.mount
    
Assuming that you have a /some_other_disk mount with more room:
    mkdir /some_other_disk/gnu
    rsync -va /gnu/store /some_other_disk/gnu/
    
Move the old store create the correct directory for the new
    cd /gnu/store
    mv store store.old
    mkdir store
    chmod 01775 store
    chown root:guixbuild store
    
Change the Guix configuration file - /etc/systemd/system/gnu-store.mount - under [Mount]:
    What=/some_other_disk/gnu/store
    
Reload configuration and restart the daemon
    systemctl daemon-reload
    systemctl start guix-daemon.service
    systemctl status guix-daemon.service
    systemctl status gnu-store.mount

When you're sure everything looks good
rm -rf /gnu/store.old

Like I said this worked and guix pull/install/etc worked fine afterwards
- previous installs were recognized etc.

When I ran:
guix gc --verify

It returned success (0 ret code)

I noted however that the new /gnu/store was approx double in size - it
looked like it had created new links to represent store items.

I then ran:
guix gc --collect-garbage

This seemed to remove about half the size of the new store - suggesting
to me that stale links were now removed.

Is my method sane?

Is there a better way of doing such a move to avoid the doubling of size?


Thanks,
Phil