[PVE-User] Why are images and rootdir not supported on CephFS?

[Fabian Grünbichler]

On February 16, 2020 5:26 pm, Frank Thommen wrote:
> Thank you for the link.
> 
> Even though Fabian Gruenbichler writes in the bugreport 
> (https://bugzilla.proxmox.com/show_bug.cgi?id=2490#c2) that Ceph RBD 
> offers all features of CephFS, this doesn't seem to be true(?), as 
> CephFS supports "vztmpl iso backup snippets" and Ceph RBD "images 
> rootdir" (https://pve.proxmox.com/pve-docs/chapter-pvesm.html), so these 
> two storage types are complementary and RBD cannot replace CephFS.

that comment was about using CephFS for guest image/volume storage. for 
that use case, RBD has all the same features (even more), but with 
better performance. obviously I didn't mean that RBD is a file system ;)

> What would be a good practice (CephFS and RBD are already set up): 
> Create an RBD storage on the same (PVE based) Ceph storage that already 
> has CephFS on top of it and use one for templates and backups and the 
> other for images and rootdir?

yes

> Won't it create problems when using the same Ceph pool with CephFS /and/ 
> RBD (this is probably rather a Ceph question, though)

you don't use the same Ceph pool, just the same OSDs (pools are logical 
in Ceph, unlike with ZFS), so this is not a problem.

> Additionally this might create problems with our inhouse tape backup, as 
> I don't think it supports backing up object storage...

the usual backup options are available - use vzdump, and then backup the 
VMA files. or use some backup solution inside the guest. or both ;)