Xtrabackup rsync question

Quick question:

The XtraBackup documentation warns to mount NFS mount points in SYNC mode.

Just want to make sure that if I backup to local storage and THEN rsync to a remote NFS storage solution, that requirement is no longer an issue.

The problem still persists in case you run --prepare on a different machine, some data might still remain on the source server OS file cache.

The remote NFS share would only copy the completed backups via rsync. Any --prepare would be done on a Recovery VM after the backups would have been copied back over from the NFS share (probably with rsync again).

In that scenario, would I be ok with NOT mounting the NFS shares in SYNC mode?

The issue is with --backup and --prepare being done in different machines, which seems to be the case here.

But I tested that successfully… I have a cron job on my Backup server that fires off a script, and that script launches remotely (via ssh) the xtrabackup job on the MySQL server, streaming the backup to the Backup server.

The Backup server also have a MySQL server, and I did the --prepare and --move-back on it and was successful at starting/accessing my database.

I was under the impression that you did NOT have to do the --prepare on the same machine as the --backup, and my testing seemed to indicate that it was indeed the case.

Also, can XtraBackup 8 do --prepare on backups streamed from a XtraBackup 2.4?

If I have a mix of XtraBackup 8 and XtraBackup, can they all stream to the same Backup server? Can a single machine be used to --prepare both, or do I need two different recovery VMs (one in 2.4 and one in 8)?