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Re: [Xen-users] iSCSI and LVM

To: Bart Coninckx <bart.coninckx@xxxxxxxxxx>, Xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] iSCSI and LVM
From: Jonathan Tripathy <jonnyt@xxxxxxxxxxx>
Date: Mon, 14 Jun 2010 22:42:41 +0100
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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
you may also find
type=pdf interesting



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

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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