Re: [Xen-users] Xen and iSCSI

[Markus Hochholdinger <Markus@xxxxxxxxxxxxxxxxx>]

Hi,

Am Sonntag, 29. Januar 2006 22:58 schrieb Alvin Starr:
> Markus Hochholdinger wrote:
[..]
> >well, my idea of HA is as follows:
> > - Two storage servers on individual SANs connected to the Xen hosts. Each
> >storage server provides block devices per iscsi.
> > - On domU two iscsi block devices are combined to a raid1. On this raid1
> > we will have the rootfs.
> We are doing doing this. Well sort of.
> We are having the dom0 attach to the iscsi devices and then pass them up
> as hda/hdb. The domU's deal with the raiding of the devices.

And the domU makes the raid1?


> My reason for doing this is that the domU's don't need any access to the
> network that contains the iscsi devices and has all the iscsi
> information hidden from them so that they don't know anthing about the
> arrays.

Yes, thats a good point.


>  All my dom0's have access to the all the iscsi devices so that
> migration is possible.

But you have to take care that no two dom0s write to the same iscsi target!


> I have done the resync thing to upgrade the storage server software. It
> is a pain but it is do-able.

Sounds not that good i hoped.


> The other advantages hold true even if the dom0's attach to the iscsi
> devices.

Yes.


> >Disadvantages:
> > - When one storage server dies ALL domU have to rebuild their raid1 when
> >storage this storage server comes back. High traffic on the SANs.
> > - Not easy to setup a new domU in this environment (lvm, iscsi, raid1)
> Rebuilding the arrays can suck back a lot of network bandwidth. It is
> much better to rebuild the raid arrays consecutivly. rebuilding them
> concurrently really slows things down and causes the drives in the iscsi
> targets to really go mad seeking.

OK.


> building a new domU is quite easy.
> I build the raid array in the dom0 and then mount it locally and extract
> a minimal install onto the array. I then unmount the array and stop the
> raid. I can then boot the domU.
> then ..... bob's your uncle.

It is easy to handle for the domUs.


-- 
greetings

eMHa

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