Re: [Xen-users] iSCSI and LVM

[Bart Coninckx <bart.coninckx@xxxxxxxxxx>]

----- Original message -----
>
> 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?
> > >
> > > _______________________________________________
> > > Xen-users mailing list
> > > Xen-users@xxxxxxxxxxxxxxxxxxx
> > > http://lists.xensource.com/xen-users
> > >
> > >         
> > 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...

It's your call but i would definitely testdrive this first. People are going to put their websites on these and expect them top erform adequately- even for fiew bucks.

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