Divide "catastrophic" into 2 categories. one is with your virtual payload and one is with your infrastructure. Consequently, its good practice to keep payload and infrastructure separated in terms of storage.
when something catastrophic occurs...
Backing up PVE in itself is not all that useful or even desirable, and should be downright avoided if a member of a cluster- cluster members are cattle not pets.
If you DO want to back up the host (lord knows why) any linux backup method would...
No. that functionality is dependent on your hardware, and might need some intelligence/built tooling by the operator. PVE isnt a storage device.
yes. as a matter or fact, ANY filestore can be used for backup (a SAN would need a local resource to...
that doesnt really mean much. Centos 7 may not be further maintained (EOLed) BY REDHAT but that doesnt mean that downstream users cant backport and maintain their software on their own. its just more work. IBM's decisions to not provide resources...
those two things are not mutually exclusive. xcp-ng uses centos for its baseos and userland apps. see https://xcp-ng.org/blog/2020/12/17/centos-and-xcpng-future/
worth noting that xcp-ng version at that time (2020) was 8.2, and as of 8..3...
so lets put things in perspective- your deluge problem isnt with permissions, its with a firewall.
As for permissions in general, the relevent factors will be of WHO owns your processes; this will be different depending on whether you are using...
Thats an understatement. You have yet to provide ANY argument, data, or reason to validate that assertion. it kinda makes the whole table pointless since you make conclusions without any need for the table.
the ceph documentation has a dedicated page for pg troubleshooting: https://docs.ceph.com/en/latest/rados/troubleshooting/troubleshooting-pg/
this is also a good resource: https://ceph.io/geen-categorie/ceph-manually-repair-object/
generally...
zfs and btrfs have similarity, but are not the same. Their LVM component CAN handle vdev distribution (eg, raid) but do not have to.
The reason you dont want to put zfs and btrfs on top of raid is the potential for egregious write amplification...
ZFS replication isnt a replacement for proper shared storage as it is asynchronous. a small cluster should be 2 real nodes, 1 quorum, and external shared storage (block or file)
If Ceph doesn't let you write is because some PG(s) don't have enough OSD to fulfill the size/min.size set on a pool. In a 3 host Ceph cluster, for that to happen you either have to:
Lose 2 hosts: you won't have quorum neither on Ceph nor on PVE...
so... how do you qualify "stability" as a feature? do you have metrics comparing to other hypervisors? I'm not saying this is wrong, its just not present in your comparison matrix as such.
As for VM backup with "important" functions- the ones...
Its POSSIBLE to do what you ask. but I wouldnt, because ceph is pretty sensitive and trying to keep parts of the cluster with one central configuration AND the rest synchronized is quite failure prone.
This wouldnt work anyway. you need the same...