IBM SVC definitely does NOT support SCSI unmap and we would not pass them through to back end disk if we got them.
Actually if SVC layer sees an unmap command it actually ignores it.
IBM SVC will do zero-detect where if a write contains nothing but zeros and the target disk is space efficient, then the write will not be destined to disk. Instead the B-Tree will be updated to say those grains are now free, but the grains are not released, meaning no space is reclaimed. The only way to reclaim space is to do a VDisk copy (which is way too much work).
in-Band LUNs are image mode, so if VMware DID write zeros,
they would be written to disk by SVC layer (rather than be dropped).
I don't know how 3PAR zero detect works, but maybe it releases space immediately (rather than just do b-tree update).
If so, that would have worked OOB as well as IB.
Actually if SVC layer sees an unmap command it actually ignores it.
IBM SVC will do zero-detect where if a write contains nothing but zeros and the target disk is space efficient, then the write will not be destined to disk. Instead the B-Tree will be updated to say those grains are now free, but the grains are not released, meaning no space is reclaimed. The only way to reclaim space is to do a VDisk copy (which is way too much work).
I don't know how 3PAR zero detect works, but maybe it releases space immediately (rather than just do b-tree update).
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