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Space Reclamation On Thick Provisioned LUN/Volume - Vaai Unmap


This has probably been answered several times but i can't find anything for Thick lun/volumes. Maybe I have a misunderstanding of what a thick netapp lun is. Our vsphere environment is provisioned with Thick volumes that contain a Lun (1:1) with space reservation enabled. Hence I think these are Thick LUNs, please correct me if I am wrong. Running ontap 9.1 with ESXi 6.0 and vmfs 5


I was going to manually run the unmap command from the esxi to reclaim space after noticing that space was not being given back to the lun/volume (expected on vmfs -5) backing the datastore and noticed that it is not supported:

esxcli storage core device list -d naa.600a098038303049332b454a516b504e

Thin Provisioning Status: unknown
Attached Filters: VAAI_FILTER
VAAI Status: supported

esxcli storage core device vaai status get -d naa.600a098038303049332b454a516b504e

ATS Status: supported
Clone Status: supported
Zero Status: supported
Delete Status: unsupported

I did noticed that space allocation is not set on the lun, but based on this netapp doc I think it is only meant for Thin luns and i think mines are Thick. 

All i am trying to do is to give the space back to the storage when I Svmotion or delete a VM, and based on the size of some of the volumes is has never been done. Now, will enabling space allocation on the lun work even though it says it is only for thinly provisioned ones. If it does, i dont see the point of doing it becasue ill have to offline the lun to do so, but it will be good to know for future luns.

What am I missing? What are my options?


Thanks in advance!


Re: Space Reclamation On Thick Provisioned LUN/Volume - Vaai Unmap


You have "space reservations" on the level of Vmware and Netapp.


What is the difference between thin/thick provisioning.  Interprete thin as being not reserved and thick as reserved space in the aggregate. So when you have a thick provisioned volume of 10GB in an aggregate of 100GB (I know this is small but just for the explanation) then 10% of the space is reserved cannot be used by other volumes.  You will notice 90GB is still available in the aggregate. If you create thereafter another THIN provisoned volume of 15GB, you still would have 90GB available in the volume.

The same is valid for a LUN. When having a volume of 100GB and you create thick provisioned LUN of 80GB then only 20GB would be availalbe in the volume....


Hope this is clear. 


As you can have space reservations within Vmare and Netapp, I ould advice to use always thick provisioning within Vmware. For the Netapp you can choose between thick of thin provisioned volumes depending on the availability of storage space. LUN's on Netapp I would suggest always THICK provisoned...


Hope it helps

Re: Space Reclamation On Thick Provisioned LUN/Volume - Vaai Unmap


Thanks for the clarification. That is exaclty how i thought it worked.

Now, my other question is how does space reclamation work in my case (thick provisoned LUNs). From all the articles i read it only seems possible on thin provisioned luns, or am I wrong. Before I attempted to manually reclaim space i followed vmware recomendations to make sure the LUN backed DS supported SCSI unmap commands (Delete) and it seems it does not(see first post for results). 

As I said my main goal is to return space to the storage. I know i can always create a new thick volume (Netapp) and S-vmotion to it and delete the old one to reclaim space but that is not efficient when you have a bunch of DS.


Re: Space Reclamation On Thick Provisioned LUN/Volume - Vaai Unmap


You are right. THe space is given back to the aggregate only when the LUN is thin provisioned. But using thin LUNs ...for me this is rather dangerous because the LUN might go offline because of lack of space in the aggregate. Might be interesting to look at https://library.netapp.com/ecmdocs/ECMP1196784/html/GUID-6AD84908-041A-497D-95A7-BB6AFDD1B282.html


This is one of the reasons why working with NFS-datastores within a Vmware-environment makes life easier... 🙂 I only use LUN's in case NFS is not possible....

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Re: Space Reclamation On Thick Provisioned LUN/Volume - Vaai Unmap


Thanks for your help and recommendations.


That’s one of the kb I read where I noticed it may be only for thinly provisioned luns.


thanks again.

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