Easy way to merge Virtual Disks in Microsoft's iSCSI Software Target?

Inherited client.

They have 2 VMWare ESXi 5.5 hosts. Both hosts have local storage.

Both hosts also share two external, iSCSI, storage platforms. The two external are as follows:
Dell PowerEdge 2950 - running FNAS and presents as one 3.96TB LUN. This LUN is setup on both VMWare hosts and therefore VM's can move between the hosts as required
Dell PowerVault NF500 - running Windows Server 2008 R2 Enterprise
On the PowerVault server using Microsoft's iSCSI Software Target, they split a 2TB disk into two separate LUNs;
1.JPGThis LUN is presented to VMWare Host1:
2.JPGThis LUN is presented to VMWare Host2:
3.JPGI would prefer to have the 2TB disk presented on one LUN and then use that as proper shared storage for VMWare hosts, rather than the way it is at present.

My question is, can I merge the two Virtual Disks without affecting the data within those Virtual Disks and then present that as one iSCSI LUN to the VMWare hosts?

Or will I need to backup everything on both LUNs, kill the Virtual Disks, reconfigure the Virtual Disks as one Virtual Disk and have that presented to the VMWare hosts?

Any guidance would be helpful
LVL 13
Mark GalvinManaging Director / Principal ConsultantAsked:
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Cliff GaliherCommented:
There is no good way to merge disks. You could save yourself *some* time killing just one virtual disk and then expanding the other and restoring the data. Since this is still a destructive change, I would *not* skip backing up the disk you will be expanding though. At only a terabyte, that shouldn't take too terribly long with proper fast storage available for backup/restore.

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There are merge partition utilities from Paragon and Easus that may work,but you never know until you try.
Cliff GaliherCommented:
Microsoft's iSCSI target software uses the VHD file format internally to present logical units to iSCSI initiators. Partition utilities work on partitions on an existing disk. But that is wholly a different scheme and data manipulation. Merging data in this case would require merging the underlying VHD files, but because the VHD format also includes metadata. Partition software (including the ones mentioned above) do not work with VHD files. There are a couple of VHD file manipulation tools on the market, but last I checked, none merge VHD files, and all are doing things using unsupported manipulation below the file level using undocumented APIs. I'd strongly recommend against that route.
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I guess we're also looking at a vhd size limitation too in that a vhd won't go any larger than 2048 gb .
So merging the two would require a vhdx file since he has two 2048 gb partitions.

All though this looks interesting.

Mark GalvinManaging Director / Principal ConsultantAuthor Commented:
Thanks both.

We have decided to:
Backup the relevant VM's with Veeam (already in place)
Shut down the VMs on Host 1's PowerVault Data Store
Move those VMs to the FNAS shared storage
Delete the VHD which is presented to Host 1
Back up the VM's on Host 2's PowerVault Data Store
Expand Host 2's VHD
Move the VM's from the FNAS Data Store back to the newly expanded VHD

This way everything is backed up in case something goes wrong.

Will post outcome.
Mark GalvinManaging Director / Principal ConsultantAuthor Commented:
Moved the smallert datastore, killed that VDisk, expanded the other and moved the data store back. All working now.
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