We currently have about 10K accounts using 900GB in /opt/zimbra/backup. We need to migrate this to a new storage. We are using hard links as in previous versions. Transferring via rsync is taking several days and rsync doesn't seem to like when new nightly backups run. So one option would be to disable backups until everything gets copied.
Another option I thought about would be to mount the new storage under /opt/zimbra/backup and the old storage under another directory. But would I be able to switch between the two directories if I need to restore from an older backup set?