We are currently running a 3-node vSAN 6.5 cluster with approximately 14TB of usable space. As shown below, it shows 7.42TB Used - Physcally Written and 4.8TB Used - VM overreserved. The default storage policy is being used and Object Space Reservation is set to 0 and dedup and compression are disabled. Anyone have any idea why this Used - VM overreserved is occupying this space?
How many VMs do you have in this environment? Large VMs (RAM)?
What you are seeing is most likely vSAN Sparse Swap. If you add all the memory of VMs (turned on) and multiply by 2 you will most likely get to your overreserved number. The reason? By default, vSAN thin-provisions in the back end; however, this does not apply to the swap file, and this is thick provisioned. To take it a step further, this object (swap) utilizes the default policy (FTT=1 default setting). This mean that the swap object in vSAN will be size of memory of VM * 2 (FTT=1). If you change the FTT on the default policy then the amount of space used will increase (FTT=2 & 3).
If you do not wish to have this space taken, you can disable SwapThickProvision advanced setting on the hosts.. Proper planning should be done prior to disabling this. I wrote a blog about this not long ago. https://greatwhitetec.com/2017/03/20/vsan-sparse-swap/
The VM overreserved setting appears when dedupe/compression is disabled. I did a quick test on my lab to demonstrate this.
- Lab hosts had SwapThickProvisionDisabled set 0
- Space of VM overreserved = 40GB
- Changed /VSAN/SapThickProvisionDisabled to 1 (see my blog for how to..)
- Turned VMs off/back on
- Space of VM overreserved now = 0GB
Hope this helps. I will write a blog about this too shortly...
