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

To: Adi Kriegisch <adi@xxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] iscsi vs nfs for xen VMs
From: Rudi Ahlers <Rudi@xxxxxxxxxxx>
Date: Thu, 27 Jan 2011 13:40:26 +0200
Cc: yue <ooolinux@xxxxxxx>, Christian Zoffoli <czoffoli@xxxxxxxxxxx>, "xen-users@xxxxxxxxxxxxxxxxxxx" <xen-users@xxxxxxxxxxxxxxxxxxx>
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Reply-to: rudi@xxxxxxxxxxx
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On Thu, Jan 27, 2011 at 1:04 PM, Adi Kriegisch <adi@xxxxxxxxxxxxxxx> wrote:

>> What do you then do if you want redundancy, between 2 client PC's, i.e
>> similar to RAID1 ?
> Oh well, there are several ways to achieve this, I guess:
> * use dm mirroring on top of clvm (I tested this once personally but did
>  not need it for production then -- will probably look into it some time
>  again).
>  I think this is just the way to go although it might be a little slower
>  than running a raid in domU.
> * Giving two LVs to the virtual machines and let them do the mirroring with
>  software raid.
>  I think this option offers greatest performance while being robust. The
>  only disadvantage I see is that in case of failure you have to recreate
>  all the software raids in your domUs. In some hosting environments this
>  might be an issue.

Why not just give the 2 LV's to the dom0, and raid it on the dom0
instead? The the domU's still use the "local storage" as before and
they won't know about it.

> * Use glusterfs/drbd/... Performancewise and in terms of reliability and
>  stability I do not see any issues here. But to use those you actually do
>  not need a SAN as a backend. A SAN always adds a performance penalty due
>  to an increase of latency. Local storage always has an advantage over SAN
>  in this respect. So in case you plan to use glusterfs, drbd or something
>  like that, you should reconsider the SAN issue. This might save alot of
>  money as well... ;-)

I would prefer not to use DRBD. Every layer you add, adds more
complication at the end of the day.

And we already have this expensive EMC SAN, so I would like to utilize
it somehow, but with better redundancy.

> -- Adi
> _______________________________________________
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Kind Regards
Rudi Ahlers

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