I made some related comments about this here:
https://forum.proxmox.com/threads/proxmox-backup-server-3-0-available.129717/#post-568741
https://forum.proxmox.com/threads/u...tible-with-proxmox-ve-8-0.132991/#post-585500
And I thought I had a better post w.r.t. this around, but could not find it.
We really need to better encode the answer to this compatibility question and our general guarantees in the documentation's FAQ.
Backup protocol and format did not change, so there's still full forward and backward compatibility in regard to that.
Proxmox Backup Server 2.2 added the support for namespaces, Proxmox VE 6 can only back up to the root namespace and also only restore from that, nothing change w.r.t. this in Proxmox Backup Server 3, i.e., for Proxmox VE 6 the same limitations as previous still hold (it's EOL after all), but newest Proxmox VE 7 and Proxmox VE 8 can use all features from both Proxmox Backup Server 2 and 3.
In general, we will:
- keep support for reading older backup formats, if we ever need/want to introduce a new one, so restoring existing backups made to new systems will always work.
- try hard to keep backward compatibility for the protocol to create and read (restore) backups, at least for the current and last matching releases we will guarantee that. Meaning, a client that is one major release behind should be still able to back up and restore what they could do previously from a server that is the same major version, or one version older or one major version newer, but not necessarily if the server is two major versions newer. E.g., while currently one can still backup from Proxmox VE 6 to Proxmox Backup Server 3, which is two major versions newer, that
might change with future PBS 3.x point releases; albeit it's not planned and if there isn't a good reason/benefit we won't just break it.
- ensure that the Proxmox Backup Server API stays compatible for the current and the previous matching Proxmox VE release, older might continue to work, but that's supported on a best-effort basis.
So the more permanent table could look like the following, where Proxmox Backup Server X and Proxmox VE Y are based on the same Debian major release.
Backup / Restore | Proxmox VE Y - 1 | Proxmox VE Y | Proxmox VE Y + 1 |
Proxmox Backup Server X - 1 | Full Support | All but new major Features | Best Effort |
Proxmox Backup Server X | All but new major Features | Full Support | All but new major Features |
Proxmox Backup Server X + 1 | Best Effort | All but new major Features | Full Support |