topic LUN SPACE CONFUSION in ONTAP Discussions

LUN SPACE CONFUSION

NAYABRASOOL — Thu, 05 Jun 2025 06:19:31 GMT

Hi All,

I have got an alert for my volume threshold reached as the space left on volume was only 12MB out of 107MB i have lun on top of this Volume which is of size 102MB, i have conveyed the client about this but he was telling the lun what he is using on the windows side it was showing 61.1 MB free , so could anyone please explain about this.

Thanks,

Nayab

Re: LUN SPACE CONFUSION

pinrell — Fri, 07 Sep 2012 10:32:15 GMT

Hello

Could be several things,

Mainly snap residing within the volume:

It is a Lun thinprovisioning??,

Has fractional_reserve =???

Reserve for Volume Snap?

Re: LUN SPACE CONFUSION

GARDINEC_EBRD — Fri, 07 Sep 2012 10:38:32 GMT

I'm sure there are KB articles about this, but don't have time to go hunting right now, sorry.

As a quick example, if you delete a load of data from the client-side (eg NTFS) the client marks the blocks as free, as opposed to physically zero'ing out the data, right? Down at the storage level WAFL has no way to know these blocks have been deleted, so when you write more data to the LUN it will consume new blocks in the volume. Typically, as a LUN ages, you will find the NetApp side will show the LUN at, or close to 100% full, but the clients filesystem may still have plenty of space. This is by design, and often not a problem - although it looks a bit odd at first. Check out Snapdrive's Space Reclaimer feature if using Windows - this will reclaim those free blocks at the WAFL end if required. Docs around this will also explain why you see the difference in more detail than I've done so here.

Regards,

Craig

Re: LUN SPACE CONFUSION

NAYABRASOOL — Fri, 07 Sep 2012 13:12:20 GMT

Thumps Up !!!!! Craig Thanks a lot ,

As i am new to Netapp i don't have idea about this stuff , can you provide me the link to that KB article about which you are speaking please.

Regards,

Nayab

Re: LUN SPACE CONFUSION

saranraj456 — Sat, 08 Sep 2012 05:21:40 GMT

Provide the o/p of lun show -v

Re: LUN SPACE CONFUSION

SNETAPPUSER — Sat, 08 Sep 2012 05:46:18 GMT

GARDINEC_EBRD is correct. Use SnapDrive for windows to reclaim free space from thin provisioned LUNs from a Windows box. If you encounter the same problem with VMWare, you have to do it manually using SCSI UNMAP commands in ESXi shell. Here is a KB article for that. http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2014849 (Note that, your storage system should support VAAI capability.)