[pbs-devel] [PATCH proxmox-backup v13 03/26] pbs-api-types: add backing-device to DataStoreConfig

[Thomas Lamprecht]

Am 17.11.24 um 20:27 schrieb Thomas Lamprecht:
> note: this pen drive is brand new, got just unwrapped and passed through to my dev
> VM, and as such it's still coming with the formatting from factoring.
> 
> Now, I first did not even expect that it shows up in the selector, but it did, so I'm
> wondering if it either should not be available or if it should work to use this disk
> too.

For the record, the main blocker here are:

1. that exfat/vfat does not support arbitrary UID/GID for files, so a datastore creation
   fails when PBS tries to assign the directories and files ownership to the backup user
   and group. While not really nice, that can be worked around by using the 
   `-ouid=34,gid=34` mount options.

2. more importantly, a too low max dentry per directory limit, causing ENOSPACE errors
   on chunkstore creation. While this could be workarounded by creating deeper chunkstore
   levels with fewer directories per level, e.g. a three-letter prefix per level, which is
   coming out a 3 * 4 bits = 12 -> 4096 directories per level, and that for three or four
   levels. But that's rather a bigger change, and having different layouts per filesystem
   type sounds like it could cause quite a few issues, not what one wants for a stable
   backup solution.

3. Maybe more? we did not get around to even create a datastore, so actual usage and
   support for locks and all that might be other blockers.

So it's simply not feasible to support vfat, or other limited FS.