VMware have just released vSphere 6.7 and there are many compelling reasons to upgrade, one of them is the improvements they have made to the UNMAP behavior, this has been developed with us at Dell EMC on an XtremIO array in order to ensure maximum performance.

If you are new to the whole UNMAP story, I suggest you start here


and here https://volumes.blog/2015/04/28/vsphere-6-guest-unmap-support-or-the-case-for-sparse-se-part-2/

and here https://volumes.blog/2017/07/28/vsphere-6-5-update-1-is-out-heres-why-you-want-to-upgrade/

ok, you now should be familiar with the behavior..so what’s new?

ESXi 6.5 and prior set unmap priority to “low” as default. translates to 25MBps of unmap rate. ESXi 6.7 changes the unmap rate to best of array’s capability. This allows customers to configure a higher UNMAP rate for arrays that can handle a higher UNMAP rate w/o impact to VM IO.

The unmap progress can be monitored on the VC UI (along with the existing vsish on a host’s command line).

Select a host, and go to “monitor” -> “performance” -> “advanced” in the VC UI. Click on “chart options” and select “datastore”  and at the bottom of the list, “unmap size” and “unmap IOs” are available to be selected.

Selecting these starts showing interval stats for unmap on available datastores”

Automatic UNMAP support for SESparse

SEsparse is a default format for all delta disks on the VMFS6 datastores. On VMFS5, SEsparse is used for virtual disks of the size 2 TB and larger. SEsparse is a format similar to VMFSsparse with some enhancements. This format is space efficient and supports the space reclamation technique. With space reclamation, blocks that the guest OS deletes are marked. The system sends commands to the SEsparse layer in the hypervisor to unmap those blocks.

In ESXi 6.7, on VM’s with SESparse snapshot (SESparse is default snapshot format on VMFS6), the space reclamation has been made automatic. 

Using the new vSphere bits, one can check UNMAP or space recovery for SESparse is automatic.  To test this feature you need to delete files from guest OS  which is on SE Sparse snapshot disk and check space getting automatically reclaimed on disk.

How do you run the unmap command?


Or via the UI (HTML5 only)

How do you check if the new setting has been applied?

You can now also monitor the UNMAP bandwidth from the vCenter H5 UI as well!


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