Re: [Xen-users] Storage alternatives

[Javier Guerra <javier@xxxxxxxxxxx>]

On Fri, Mar 13, 2009 at 8:22 AM, Jan Marquardt <jm@xxxxxxxxxxx> wrote:
>
>> IOW: the iSCSI initiator and RAID (i guess it's RAID1) should be on
>> Dom0, and the DomU configs should refer the resultant blockdevices.
>
> This is one solution we are discussing at the moment, but I think it would
> be a lot smarter to get the raid functionality on a layer between Âthe
> harddisks and the iscsi targets as adviced by Nathan.

yep, that further reduces duplicated traffic.  i didn't mention this
just because i'm not too familiar with DRBD, and because i thought
it's too different from your current setup, so you might want to go in
steps.  if it's easier to redo it all again, this is a better idea.

>> Agreed. ÂYou could even potentially move the mirroring down to the
>> storage nodes (mirrored nbd/etc. devices) and HA the iSCSI target
>> service itself to reduce dom0's work, although that would depend on you
>> being comfortable with iSCSI moving around during a storage node
>> failure, which may be a risk factor.
>
> I think that we would have to reboot each domU in this case after a failure,
> isn't it? The goal is to have domUs which would not be affected by failure
> of one storage servers.

that's one reason to put all storage management as low on the stack as
possible.  in this case, Dom0 should be the only one noting the
movement, and any failover detection (either RAID1, multipath, IP
migration, etc) should finish at Dom0.  DomUs won't feel a thing
(unless it takes so long that you get timeouts).

>> Abstract your disks and iscsi exports; then use ZFS on two pools this will
>> minimize the administration.
>
> ZFS seems to be very nice, but sadly we are not using Solaris and don't want
> to use it with FUSE under Linux. Nevertheless does anyone use ZFS under
> Linux and can share his/her experiences?

ZFS gets you some nice ways to rethink about storage, but on these
cases it's (mostly) the same as any other well-thought scheme.


-- 
Javier

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