[Xen-users] Advice on redundant SAN/NAS storage for Xen

[Chris 'Xenon' Hanson <xenon@xxxxxxxxxxxxxx>]

  This isn't super Xen-specific, but it's the basis on which I'd like to build 
my Xen
cluster storage.

  I'm planning to expand my Xen servers at my datacenter into a cluster with 
high
availability and reliability. As part of this, I want to move all DomU storage 
to a common
SAN or NAS infrastructure and make all the Dom0s basically identical. In this 
way, I can
move DomU's around between Dom0s as needed for performance or reliability 
reasons. If a
Dom0 server fails, I can just bring up its DomUs on different servers with no 
loss.

  So, to do this, I need fast block-access to a networked storage device. To 
avoid
single-point of failure, I'd like this storage device to be a pair of discrete 
devices,
each connected to all Dom0 machines via a pair of networks. This way, I can't 
lose the
whole thing through the failure of one storage device or network cables or 
switches.

  What I can't put together in my mind is all the pieces. We have RAID and SAN 
and NAS and
LVM and Xen and monkeys and bears oh my.

  The best design I can think of is this:

Two machines running Linux configured as SANs, using something like ATA over 
Ethernet
(AoE) to link them to a pair of GigE switches that then link to every Dom) box. 
The pair
of SAN boxes each export a block of raw storage that the Dom0 machine then 
RAIDs together
as RAID1 and provides to Xen and the DomU as a block device. The Dom0 gets
network-portable storage, with RAID reliability and redundancy.

  The other way might be to have the Dom0 and Xen pass through both block 
devices to the
DomU and let the DomU RAID them together. I'm not sure if either is better. 
Maybe RAID on
the DomU would allow the DomU to be migrated easier?

  Is there a better and less messy way to provide redundant SAN-type storage to 
Xen DomUs?
The main criteria are:

  Immune to failure of a single switch or SAN box.
  Allow DomUs to be moved seamlessly to other Dom0s without messy 
reconfiguration.


  Suggestions from anyone who has done it before?

-- 
Chris 'Xenon' Hanson, omo sanza lettere                  Xenon AlphaPixel.com
PixelSense Landsat processing now available! http://www.alphapixel.com/demos/
"There is no Truth. There is only Perception. To Perceive is to Exist." - Xen

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