Invoke-NaHostVolumeSpaceReclaim - How does it work?

[RFRANGEUL]

Hello,

I am writing a Powershell script to reclaim space on my Windows servers having iSCSI LUN.

My script calls the Powershell cmdlet "Invoke-NaHostVolumeSpaceReclaim".

The toolkit does not give many informations about this cmdlet and i am curious to understand how does it work.

Does this cmdlet execute "hole punching" on unused blocks?

Or
Does it contact directly NetAPP array to release blocks?

Rgds

[cknight]

Hello, Rfranfeul.  If I understand your questions, the answer is yes to both.

This cmdlet uses Windows APIs to read the NTFS block table and uses in-band SCSI UNMAP commands to punch/release each free range.  Care is taken to ensure NTFS does not allocate space in the empty ranges during the operation.  I believe that WS2012 can do this natively, but earlier versions of Windows benefit from running this cmdlet regularly so that thin-provisioned LUNs remain space-efficient.

[RFRANGEUL]

Hi Clinton,

Thanks for your answer.

So, this cmdlet uses SCSI UNMAP commands to release unused blocks.

Is it the same mechanism for the Space Reclamer embedded in SnapDrive?

Rom

[cknight · Accepted solution]

There are multiple ways to unmap blocks in ONTAP, including the standard UNMAP, an earlier vendor-specific SCSI CDB, and out-of-band ONTAP APIs.  The cmdlet uses UNMAP but can fall back to the older CDB if necessary.  I don't know which method SnapDrive uses.  I do know that when I wrote the cmdlet, it was much faster than SDW, but that may have changed.

[RFRANGEUL]

Hi  Clinton,

Thanks for your reply.

Rom