XP Migrating repo on a live server

Hi, we have a large repo that needs to be migrated to a new drive, on a live server.
What is the optimal way to migrate the data to maintain consistency and avoid downtime?
We tried with using rsync but it takes 2-3 hours to go through the entire repo, so even when there are no transfers it takes so long because of the amount of files and directories.
So the scenario rsync -> stop xp -> rsync -> start xp is involving over 2 hours of downtime, that is not a good option.
What would be the best way to prepare for migration? How to shrink the repository so it uses just the minimum amount of files?
Is there any way to shrink the repository by deleting unused versions?

Upgrading to xp6 will shrink repo size if there are many versions. Is it the blobstore you are migrating, or all of cms_home? The blobstore is append only, so you could copy everything first, then do a rsync of the optional changes later. Moving indexes is a different story…