Re: [Xen-users] iscsi vs nfs for xen VMs

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Sun, Jan 30, 2011 at 01:44:06AM +0200, Pasi Kärkkäinen wrote:
> On Sun, Jan 30, 2011 at 10:41:23AM +1100, James Harper wrote:
> > > 
> > > On Wed, Jan 26, 2011 at 11:38:52AM +0100, Christian Zoffoli wrote:
> > > > Hi,
> > > >
> > > > if you want to push on performance the best one is:
> > > >
> > > > CLVM over iSCSI
> > > >
> > > 
> > > And if you need snapshots, just over normal LVM over shared iSCSI LUN.
> > > (in this case your management toolstack needs to take care of locking LVM
> > > control).
> > > 
> > 
> > How sure are you of this? Every write to the original or the snapshot 
> > involves a potential metadata update. If the original is mounted on one 
> > node and the snapshot on another, I'm pretty sure that it would all go to 
> > crap really really quickly.
> > 
> > Have you actually tried this???
> > 
> 
> It's widely used.
> 
> Citrix XenServer (and XCP) do it like that, and also the 
> Xen based VirtualIron did it like that.
> 

Forgot to add this:

In Citrix XenServer it's the XAPI toolstack that's 
taking care of LVM locking, so only the "pool master" 
is executing LVM commands.

As long as you know you're executing LVM commands
only from a single node, you're good. No need for CLVM.

I guess you also need to refresh all the other nodes
after executing LVM commands on the primary/master node.

-- Pasi


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