Re: [Xen-users] Xen and iSCSI

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Sun, Jan 29, 2006 at 03:39:20PM +0100, Markus Hochholdinger wrote:
> 
> Am Sonntag, 29. Januar 2006 15:24 schrieb Pasi Kärkkäinen:
> [..]
> > > define better!? It is easier to set up. But if you want to use migration
> > > it becomes complicatet. If you use more than one Xen host you have to
> > > setup on each Xen host the block devices (iscsi, raid, lvm). And i'm not
> > > sure what happens if you have two active raid1 on the same iscsi devices
> > > on different Xen hosts!?
> > CLVM (Cluster LVM) is supposed to handle this.. it allows to create volumes
> > to shared storage (FC, iSCSI, etc).
> 
> ah. It sounds suspect to me but reading the clvm docs it should really handle 
> this. This is really an option.
> 
> 
> > And Xen itself handles the migration.. access to block device on host1 is
> > stopped when the access is started on host2 (after the migration).
> 
> It seems a lot of people do this this way. And there were never any problems 
> in this setup?
> 
> 
> > > > Then you could more easily upgrade the storage servers and only rebuild
> > > > the raid in dom0.. domU's wouldn't see any problems / failures.
> > > Well, rebuild will take the same amount of network traffic. I'm not sure
> > > if it is really better?
> > > My idea is to have the domU not depend on the block device configuration
> > > of dom0. So its easier to migrate domUs.
> > Personally I'd like to keep all the raid/iscsi stuff out of domU's.. to
> > keep domU's simple and easy to manage :)
> 
> OK, everyone can have his own opinion :-) Perhaps when i get deeper in the 
> setup i will agree to you :-)
> For migrating existing servers it could really be better to get the iscsi and 
> raid stuff out of the domUs. So the change to the servers will be minimal.
> 

In fact, even better would be to do the RAID in the storage arrays / servers
(=iSCSI targets), and provide multiple paths to the targets.. using separate 
network (switch) for both paths.

In the dom0 you would only set up multipath device to the shared RAID array 
(over iSCSI), and then create CLVM on top of that. No need to do the RAID in 
dom0 :)

-- Pasi 

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