Xen and storage

[Amos Shapira]

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.

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