Re: [Xen-users] iSCSI and LVM

[Jonathan Tripathy <jonnyt@xxxxxxxxxxx>]

On 14/06/10 22:17, Bart Coninckx wrote:
> 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?
>
>    
Nope, I havn't tested this yet, however this is based on a "risk model" 
and will probably never reach that high. I'm basing my VM packages on a 
"points" system. The highest package is worth 8 points, the middle 
package is worth 4 points, and the smallest package is worth 1 point. 
RAM sizes are 1024MB, 512MB and 128MB respectively. The smallest package 
will only have a drive size of 6GB, and the internet connection will be 
limited as well, so I'm basing my figures on the fact that the smallest 
VMs probably won't be used for high disk I/O use...
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