Creating Multiple Media Pools per Tape

[funkytownusa]

I want to create a new media set (Allocation: Always, Retention: Keep), with no de-duplication so that each backup is a self-contained full-backup. Given that each tape backup must reside in a pool (media set), can multiple media sets coexist on a single physical tape? Or is PBS incapable of storing multiple "Full-backups" to a single tape?

If the answer is NO, what prevents an LTO-9 tape from losing all of it's data, if a single or multiple chunks or files get corrupted? Because de-duplication relies on shared-chunks to reduce .tar size, the entire tape (filled with potentially years worth of backups) could be irrecoverable should a single shared chunk become inaccessible or corrupted.

What is Proxmox's recommended best practice for writing self-contained full backups tape so that a read error or corruption event on one snapshot does not impact any other backup snapshots on the same media?

 

[dcsapak]

you're right that pbs does does not store multiple media sets on a single tape and every backup made with it is fully deduplicated (within one media set)

The idea here is that a media-set is the smallest consistent unit, so we'd recommend having multiple media sets. Since they are deduplicated, you can store much more history in one media set than when each backup would be a 'full' backup. If you need redundancy for the media-sets, simply creating more media-sets is a good solution.

A (very) simplified example: instead of having 5 full, non-deduplicated snapshots on 5 tapes, You probably can have 5 media-sets which contain all 5 snapshots each, so the redundancy is still there with multiple media-sets an each has the full history.

Note that a single corrupted chunk only breaks snapshots which contains this chunk. Additionally you shouldn't rely on any single medium to be your only backup (3-2-1 rule).

Also, generally when storing LTO tapes correctly and the drives are good, there shouldn't be any data corruption, also because there is on tape crc/error correction built-in.