topic Decreasing LUN containg VMFS datastore.. in VMware Solutions Discussions

Decreasing LUN containg VMFS datastore..

oweinmann — Thu, 05 Jun 2025 06:48:46 GMT

Hi,

I ran into a serious problem today. One of our VMWare datastores ran out of disk space so I resized the Volume, then the LUN. I didn't pay attention to the maximum size Limit of 2TB for a VMFS datastore and received an error like:

Call "HostDatastoreSystem.QueryAvailableDisksForVmfs" for object "datastoreSystem-43668" on vCenter Server "" failed.

First I didn't even realize that this is related to the limitation of the datastore. And I started googling for the error and found nothing. What a suprise.

I resized the 1.86 TB LUN to 2.1 TB. All VM's are still running fine but now I wonder if I can decrease the size of the lun to 1.86TB without loosing or damaging the VMFS datastore?

Regards,

Oliver

Decreasing LUN containg VMFS datastore..

jjbitservices — Fri, 05 Aug 2011 09:32:35 GMT

Did you resize the Datastore in VMware also?

If yes:

In my opinion the only thing you can do is:

Create a new 1.86TB lun and move all the VM's to the new LUN.

Finally remove the 2.1TB lun.

If you didn't resize / extend the datastore you can shrink the lun as long as the last datastore block is not changed

Decreasing LUN containg VMFS datastore..

arunchak — Fri, 05 Aug 2011 09:53:47 GMT

If the VM's are important, then I think you should create a new 1.9 TB LUN, copy all the data and use this rather than taking the risk.

Once this is done you can try resizing the 2.1 TB lun

Decreasing LUN containg VMFS datastore..

oweinmann — Fri, 05 Aug 2011 12:19:44 GMT

Hi I didn't increase the vmfs datastore as I was not able to do that. So shrinking the lun should not harm the datastore?

Decreasing LUN containg VMFS datastore..

MENCHEGO1 — Fri, 21 Oct 2011 13:17:54 GMT

What was the end result for you oweinmann? I'm having the same issue as you had.

Decreasing LUN containg VMFS datastore..

macmillangm — Wed, 02 Nov 2011 19:23:10 GMT

I agree with those that suggest a new LUN. If you shrink a lun you may not necessarily decrease its size by removing free blocks. You dont know where in the lun the free space is, so shrinking it to a smaller size may create more problems than it solves. I have had this same problem a few times and I always took the most cautious path by creating a new volume/lun and emptying the contents of the old before removing it entirely.