Fix ERROR_QUORUM_NOT_ALLOWED_IN_THIS_GROUP (0x1728) on Windows Cluster

You're setting up a Windows Server Failover Cluster, and you add a disk to the cluster. You right-click that disk, go to More Actions, and then Assign Cluster Quorum. And then you get slapped with this:

ERROR_QUORUM_NOT_ALLOWED_IN_THIS_GROUP (0X00001728)
Quorum resource cannot reside in the available storage group.

This happens most often in a two-node cluster, but I've seen it in bigger ones too. The trigger is almost always the same — you've added a disk to the cluster, but the disk still lives in the Available Storage group. That's the default holding area. It's not a real cluster group you can assign quorum to. The cluster won't let you put the quorum witness there. It needs to be in a normal cluster group, like Cluster Group or a group you made yourself.

Why does this happen?

The root cause is simple: the disk is a cluster resource, but it's not a member of a cluster group that supports quorum assignment. The Available Storage group is a shadow group — it exists to hold orphaned resources. The cluster code specifically blocks quorum placement there. It's a safety catch. If you could put quorum there, and the group got deleted or went offline, you'd lose the whole cluster. So Microsoft hard-coded this one.

Another less common cause: you're trying to use a disk that's already in use by another cluster resource (like a file share). The quorum witness must be a dedicated disk — no other roles on it.

How to fix it

The fix is to move the disk from Available Storage into a real cluster group. Here's the step-by-step.

1. Open Failover Cluster Manager. Connect to your cluster.
2. In the left pane, expand Storage and click Disks. You'll see your disk listed there, usually with a status of Online.
3. Right-click that disk resource. Choose Properties.
4. Click the Dependencies tab. After you click, you should see a blank list unless some other resource already depends on this disk. If there are any dependencies, note them — you'll need to move them too.
5. Close Properties. Now right-click the disk again and choose Move > Select Group. A dialog pops up showing all cluster groups.
6. Choose Cluster Group (the default group). After you click OK, the disk moves. You should see the disk appear under Cluster Group in the Storage > Disks view, or in Services and Applications > Cluster Group.
7. Now right-click the disk again, go to More Actions, and select Assign Cluster Quorum. This time it should work. The wizard will open — just follow the prompts to select that disk as the witness.
8. After the wizard finishes, right-click the cluster name at the top of the left pane and choose More Actions > Validate Cluster. Run the quorum tests. You should see a green check for the disk witness section.

What if the disk won't move?

If the disk is greyed out or gives an error when you try to move it, check these things:

• Is the disk already used by another resource? Look under Services and Applications. If a file server or another role is using that disk, you can't move it. You'll need to either remove that role or add a second disk.
• Are both nodes online? If one node is down, some move operations fail. Bring both nodes up first.
• Is the cluster quorum already configured? If someone already set a file share witness or another disk, you might need to clear that first. Go to Configure Cluster Quorum Settings and choose Add or change the quorum witness, then select Do not configure a quorum witness to remove it. Then add your disk.

I've also seen a case where the disk had an old partition from a previous cluster setup. Open Disk Management on one node, right-click the disk, and check its style — it should be GPT with a single NTFS volume. If it's MBR or has multiple volumes, reformat it. Yes, you'll lose data, but this is a dedicated witness disk anyway — it should be empty.

Still failing?

If you're still stuck, run the cluster validation wizard from the Actions pane. Check the Storage section of the report. Look for errors like Disk not accessible from all nodes or Disk partition must be NTFS and GPT. Those are the usual suspects after the group membership fix.

And one last thing: make sure you're using Server 2016 or later. On Server 2012 R2 and earlier, the quorum witness configuration is a bit different — you sometimes have to use PowerShell. But on Server 2019 and 2022, the GUI path above works fine.