Shared storage with virtual servers

We are moving our data to a colocation facility.  We contracted with an IT firm to help plan virtualization.  There plan consists of 2 Xenservers and one Dell MD1000.  The Xenserver vms and data is replicated using Datacore software to the other Xenserver for high availability.  The caveat was found when they came to hook everything up.  We then realized the MD1000 was only cabled to one Xenserver, which, for high availability, means the MD1000 is not accessible if that Xenserver is offline.  That's not how we understood it and because of this it also can't be used to store the vm's if we desired.  They say they can cable to both Xenservers (MD1000 has 2 controllers) but that cuts the storage capacity of the MD1000 in half, since it's essentially now 2 storage arrays replicated.  We're trying to get the most space available in a high availability situation using the lease rack space (we are tight), but getting only 2TB of usable space out of the MD1000 seems like a waste of rack space/drives.  What direction should I be pointing them?  Is there different hardware or scenario that would give us the access to a shared storage device no matter which Xenserver is online?  They say it has to be cabled to at least one Xenserver so that Datacore can manage it and things like volume snapshots of the virtual servers can be stored there.  They did give a scenario where we put in another physical server and cable to it, but like I said, I'm running out of rack space.  If there is something better than the MD1000 that can be used to fulfill my expectations, then I'd just as soon return this brand new thing before we get too far.  I'm very green on this.  I'm just an administrator, which is why we contracted this out.  Any basic ideas I can throw back at them?
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Matt VCommented:
In order to have shared storage accessible to both units, you will need a Fibre Channel or iSCSI connected device.  Then the LUNs can be shared across both connecting servers.  From what I am reading, this MD1000 is just a really big external SCSI device.  It will not allow you to do HA with XenServer.

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