This is a usual behaviour of Ontap
Long back i had the same confusion seen some volumes shown threshold reached 70 % but in my windows box showing plenty of free space available. I was wondered what is happening to my storage and i found the reason why .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.
Tool to reclaim space :- Snapdrive
Automatic Reclaim at the Ontap level is possible from Cluster Mode 8.2 or later releases.
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