I am setting up a small virtual environment and I'm using a pair of Windows (HyperV) hosts and a Synology 54TB NAS for the VM storage.

I know I cannot use the same iscsi path for 2 concurrent hosts, as they will not be aware of each other and will overwrite each others files and cause problems.

What I have done instead is this...

  • I've created 1 LUN that is 54Tb in size, multi-connections enabled.

    I have added this Iscsi target to both hosts.

    I have created a 10Tb partition, labelled HOST1 and mounted it with a drive letter on Host 1.

    I've also created another 10Tb partition, labelled HOST2 and mounted it with a drive letter on Host 2.

    Neither of the Windows servers have the other servers 10Tb partition mounted.

As far as I can tell, I should avoid the problem of having the two hosts overwrite each others files, however I wanted to gauge opinion on this before a start using the environment incase there are pitfalls I have not thought of.

  • Yes it should work, but why don't you use 2 LUN? – eckes May 14 '17 at 10:36
  • I wanted to do that, but the synology won't let me - the size option is there, but set to max and disabled. :( – John May 14 '17 at 18:00
  • If that's the case, you're trying to get around an absurd limitation with a a very dirty hack. Configure the Synology box to offer either multiple targets to different initiators with LUNs attached to each, or use ACLs to restrict initiator access to LUNs within a shared target. – Spooler Mar 2 '18 at 21:15

It's not going to work reliably. NTFS (or ReFS) aren't cluster-aware file systems, multi-mount is going to destroy metadata tables immediately. Either you use SMB3 bolt-on with an arbitration thing on top (that's what Microsoft calls Cluster Shared Volume or CSVFS), or you use third-party arbiter like MetaSAN. Good story could be found here:

Trying to be clear on this - use iSCSI instead of SMB | Star Wind Software

On your place I'd just stick with either SMB3 share or one-mount-per-time scenario disabling SCSI reservations.

Best of luck!

P.S. Or you use cluster-aware file system like VMFS3/5 :)

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  • He is not mounting the filesystem concurrently, but using two different partitions which works just fine. – eckes May 14 '17 at 10:35
  • 2
    ... right up to a point when it actually fails :) SCSI reservations are per-LUN and not per logical volume. – BaronSamedi1958 May 15 '17 at 1:15
  • Hm, I was under the impression Windows only uses reservations when you set up a Cluster resource, but I could be wrong. But since it works for the original poster it looks like no reservation is happening. – eckes May 15 '17 at 1:32
  • Windows will indeed attempt to make a SCSI reservation, but it's up to the target as to how that's processed. A key requirement of configuring a shared iSCSI LUN is to at the very least effectively ignore reservation requests, with more advanced targets arbitrating those requests and guaranteeing serialization. A large negative to OPs solution is that the partition table is shared between machines. With a shared table, you must be absolutely certain to make changes only on one "master" host while the other is disconnected from the LUN - otherwise you risk corruption. – Spooler Mar 2 '18 at 21:53

You can connect 2 hosts to the same LUN, but you have to set the file system to CSVFS so that they do not corrupt the store. You can do this by adding it as a drive in Cluster management.

  • Connect the iSCSI connections on both
  • Go into Cluster Management, 'validate' the cluster so that it finds the drive and is connected to both servers, add the new drive as a resource
  • Go to the drives tab and change to CSVFS (I think its right click on the drive)

Then it will convert the filesystem and add the path to C:\ClusterStorage\{drive}

Make sure you store them at the C: path, do not assign another drive letter to the share as that will cause issues

It will always show as not initiated in drive manager on one server and online in the other (one of them is the 'host' for the drive, but it will move that if one host goes down)

Then you can store all VM files in a common place

See below for walk-through:

How to Configure Storage on a Hyper-V Host Cluster in VMM | Microsoft System Center

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