[pve-devel] introduce linked disks

[Stefan Priebe - Profihost AG]

Hi Dietmar,

sorry for the late reply.

Am 17.12.2012 07:49, schrieb Dietmar Maurer:
>> But shared disk are really usefull, I regulary use them for web cluster or
>> databases clusters.
>
> Can you provide some details? What database or what web server is able to
> use such shared disk?

The webserver or app doesn't matter. It's the fs which handles this. 
There are a lot of cluster fs out there.

Two examples:
- Oracles OCFS2
- Redhats GFS2

>> Maybe Stefan have a clear idea how to implemented shared disks?
> I guess we need to have special URIs for shared volumes, for example
>
> store1:/0/vm-0-disk-1.raw
>
> (owner is VM 0). But I am not sure if that is a good idea.

The idea is to have entries like this one:
shared_scsi1:vm-117-disk-5
shared_virtio2:vm-117-disk-9

We don't need the path as the PVE code always rely on the vm-(\d+) 
number. So my idea was to do this here too.

We need to change the code to get the next free controller id (scsiX / 
virtioX / ...).

The advantage of the shared_ entries is that snapshot code, backup code, 
... does not know about these disks so it won't try todo backups / 
snapshots of this disk.

A problem will be if i do a snapshot with memory/ram it also needs the 
old status of this shared disk.

So we need to block backups and snapshots with memory included for these 
machines.

Other / better ideas?

Greets,
Stefan