We can compress to xz while the new disks arrive. I
read that it is about 24
TB, so, we can revert to gzip in the future.
I suggested xz pretty much as an emergency fix; we don't want to delete
the files, but they do take up a lot of space.
I don't mind switching back to gzip when we have more space; in fact, I
already suggested this to schutz in private. However, if xz works okay
(and it should, since the interface is identical to gzip) we may as well
stay with it.
If it turns out to be too slow, we could consider 7z or something else
(rzip, bzip2, ..., or maybe even just gzip -9).