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

Frank Thommen f.thommen at dkfz-heidelberg.de
Mon Feb 17 21:42:11 CET 2020



On 2/17/20 7:23 AM, Fabian Grünbichler wrote:
> 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 ;)

Thank you for all the hints above.  I will go along these lines.  Still 
struggling with some Ceph concepts ;-)

frank


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