Re: [Xen-users] iSCSI and LVM

[Bart Coninckx <bart.coninckx@xxxxxxxxxx>]

On Monday 14 June 2010 22:57:00 Jonathan Tripathy wrote:
> On 14/06/10 20:03, Serge Fonville wrote:
> >>> LVM over NFS is not possible.
> >>> LVM needs to be applied to a blockdevice
> >>>
> >>> Fortunately, you can sitll use LVM on the storage server.
> >>>
> >>> NFS is often considered slower, due to that it adds an additional
> >>> layer to the communication.
> >>>
> >>> This does not necessarily negatively impact the performance in such a
> >>> way that it should be considered a deal-breaker.
> >>> If you expect to constantly utilize over 70% of your bandwidth, you
> >>> may be better of using iSCSI.
> >>> Then again, if you are utilizing that much, you should probably
> >>> rethink your setup.
> >>>
> >>> since I currently know very little about your expected load.
> >>> I can not give you a definitive answer.
> >>>
> >>> But looking into using NFS for your VMs should at least be looked in
> >>> to thoroughy.
> >>
> >> I suppose NFS requires image based access, which I understand is less
> >> performant.
> >
> > you may also find
> > http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.1.1830&rep=rep1&;
> >type=pdf interesting
> >
> > HTH
> >
> > Regards,
> >
> > Serge Fonville
> 
> That is an interesting read, which says that NFS and iSCSI are nearly
> the same for reads.
> 
> What is generally used in industry? At max capacity, my setup will hold
> up to 672 DomUs spread over 6 Xen hosts (And 3 RAID10 arrays on a single
> storage server), so clearly management is a big concern. This is where I
> feel that LVM/iSCSI based access is easier?
> 
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> 

That sounds like an awful lot of DomUs per RAID. Have you tested this? Can the 
RAID I/O deal with this?


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