Xen and storage

[Etzion Bar-Noy]

On Mon, Mar 15, 2010 at 10:41 AM, Amos Shapira <amos.shapira at gmail.com>wrote:

> 2010/3/12 Hetz Ben Hamo <hetzbh at gmail.com>:
> > Hi,
> > I have taken 3 machines for a project: 2 machines will act as Xen servers
> > and one machine will act as "storage".
> > The storage box is just a machine with few hard disks connected with a
> RAID
> > controller.
> > What I would like to do is create few Xen VM's with the fastest possible
> I/O
> > in terms of storage.
> > I have few options:
> > 1. I can create an LVM on the storage machine, create few Logical Volumes
> > and export them as NFS to the Xen servers and configure each VM to some
> file
> > images. Problem is, that file I/O with Xen is slower compared working
> with
> > LVM's.
> > 2. I can create an LVM on the storage machine, create few Logical
> Volumes,
> > and export those as iSCSI devices. I'm not sure whats the performance of
> Xen
> > with iSCSI devices exported from the storage box.
> > 3. I can create few partitions on the storage machine, export them as
> iSCSI
> > devices and do LVM on the Xen servers. Problem: I don't know how much the
> > "penalty" doing LVM on the Xen machines.
> > My question: What is the best option?
> > Thanks,
> > Hetz
>
> I don't have practical experience with hosting Xen images on SAN but
> when I researched the market for a SAN-based configuration of our
> production network (currently 20 Xen hosts hosting about 10 Xen guests
> each, doing DRBD between pairs of Xen guests and linux-ha for HA), at
> least one or two of the options I checked mentioned that if I store
> the Xen images on the SAN then it will require much higher bandwidth
> to it than if I use it just for plain data.
>

Why? Where does the secret IO arrive from?

Ez

>
> Based on this input, I'd recommend that you'll look at having the
> images on internal server disks and try to achieve HA at the xen guest
> level, then compare the performance with iSCSI hosted xen images.
>
> Hope this helps.
>
> --Amos
>
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