Welcome news for anyone using array-based thin provisioning with vSphere, VMware has introduced a new and simpler UNMAP command that can be invoke from esxcli with vSphere Platform 5.5. This will help 3PAR customers more easily perform the UNMAP process to free space on LUNs so that the array can discover and free the space on the back-end. This is a big deal for any thin-provisioned LUNs in a vSphere environment. In addition to an easier way to invoke the UNMAP, VMware has also made changes in how the UNMAP occurs on the array.
According to VMware’s What’s New document, the previous method of creating a temporary file and then informs the array the the blocks in the temporary file can be reclaimed. In the case of the 3PAR, the zero detect process then runs to identify the free space and reclaim it. With version 5.5, the reclaim allows the administrator to specify the size in blocks rather than a percentage and now the dad space can be reclaimed in increments instead of all at once – to help shops that experience performance degradation with the old method.
The new command is run from esxcli, logically under storage and VMFS.
esxcli storage vmfs unmap
The full syntax of the command is not clear yet and I’ll have to wait for my 5.5 upgrade to test or get more details.
The fact that the new UNMAP is run from esxcli makes me hopeful that I will be able to script and schedule the UNMAP to occur during non-peak hours when the maintenance would not be service affecting.
What is UNMAP and what does it do? See this post for more information.