IBM DS8880 now supports VMware SCSI UNMAP primitive. With this, storage space is returned to IBM DS8880 for another use when space is released from vSphere layer. Using this VMware’s VAAI SCSI UNMAP primitive, the VMware host notifies the storage device about freed space on a thin-provisioned LUN by sending a SCSI UNMAP command. DS8880 will release any entire extents that have been allocated within that freed space.
On DS8880, the extent size is either 16MB for small extents or 1 GB for large extents. Therefore, for any space to be released, the request must be for at least 16 MB. If the request is not aligned on extent boundaries, then only full extents contained within the requested range will be released.

For additional details, refer to the blog Space reclamation for DS8880 thin provisioned volumes using VMware’s VAAI SCSI UNMAP

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