Set Sparse Swap files for vSAN 6.2 or Greater


One of the Space Efficiency features of vSAN 6.2 that is available for both All-Flash and Hybrid configurations, is the introduction of Sparse Virtual Swap files. Swap files on vSAN by default, are created with the .vswp 100% reserved. In a thin provisioned/guaranteed capacity perspective, it could be said that they are effectively Lazy Zeroed Thick (LZT).

Virtual Swap files (.vswp) are created when a virtual machine doesn???t have a memory reservation equal to the amount of memory the virtual machine is configured to use. In short, a VM with 4GB of RAM configured, with no memory reservation will create a 4GB .vswp file. If a reservation is used, then the .vswp file will be the configured amount of memory minus the reserved amount of memory. The same VM with 4GB of RAM, along with a 2GB reservation, will create a 2GB .vswp file.


Virtual Swap files are given a Number of Failures to Tolerate setting of 1 (FTT=1) with a Failure Tolerance Method of Mirroring or FTM=RAID1 (Mirroring). As the storage policy of FTT=1/FTM=Mirroring stands, each object with that policy will require 2x the space (1 Mirror). 200 virtual machines with 4GB of RAM each (I???m thinking a small VDI deployment) with no reservations, would require 200 x (4GB + 4GB) or 1.6TB of space. That???s significant!

In cases where there is no memory congestion, and a virtual machine doesn???t use the swap file, it might be advantageous to have a swap file that is truly thin provisioned (the default in Virtual SAN).

In vSAN 6.2, we introduced an advanced host setting called SwapThickProvisionDisabled, when enabled, removes the space reservation for .vswp files. The generic syntax for this command is:

To get the setting:

To set .vswp files to thin:

Having to determine this configuration across more than a few hosts can be a bit of a pain without some scripting/automation.

Read more here:

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