KRBD vs librbd for qemu kvm vms

[Mark Adams]

Hi All,

I have done some research on this, but I can't find any resources that
answer my specific questions - so I am hoping that everyone on the list can
help out.

In one specific use case, I have a pve 5.4-11 cluster using ceph 12.2.12.
The main reason I haven't upgraded this is because of the very manual
process to upgrade ceph and this cluster has quite a few osds. Also it will
be replaced in the not too distant future.

On this version, should I be using KRBD or librbd for my qemu vms? I have
read a number of posts/articles that say it performs better as KRBD, but
then also see some which say it should only be for containers or bare metal.

Additionally if I were to switch (Tick the KRBD box for the specific RBD
storage) what is the correct procedure to apply this? Simply select it,
then reboot each node?

This is an HA cluster, so, are KRBD and librbd interchangeable between
hosts in the cluster? can I live migrate the VMs on to another node after I
enable KRBD then simply live migrate them back after I reboot before I then
do the same for the next node in the cluster?

Lastly, is the performance of KRBD really that much better? Is there any
downsides to using it vs librbd? I guess I still don't understand why there
are 2 options if KRBD performs better?

Thanks for any assistance you can all provide!

Thanks,
Mark