Something that crops up again and again when discussing vSphere designs with customers is whether on not they should enable (Inter-VM) TPS (Transparent Page Sharing) as since the end of 2014 VMware decided to disable TPS by default.

To understand if you should enable TPS you need to firstly understand what it does.  TPS is quite a misunderstood beast as many people contribute a 20-30% memory overcommitment too TPS where in reality it’s not even close to that. That is because TPS only comes in to effect when the ESXi host is close to memory exhaustion. TPS would be the first trick in the box that ESXi uses to try to reduce the memory pressure on the host, if it can not do this then the host would then start ballooning. This would be closely followed by compression and then finally swapping, none of which are cool guys!

So should I enable (Inter-VM) TPS?… well as that great IT saying goes… it depends!

The reason VMware disabled (Inter-VM) TPS in the first place was because of their stronger stance on security (Their Secure by Default Stance), their concern was a man in the middle type attack could be launched and shared pages compromised. So in a nutshell, you need to consider the risk of enabling (Inter-VM) TPS. If you are running and offering a public cloud solution from your vSphere environment then it may be best to leave TPS disabled as you could argue you are under a greater risk of attack; and have a greater responsibility for your customers data.

If however you are running a private vSphere compute environment then the chances are only IT admins have access to the VM’s so the risk is much less. Therefore to reduce the risk of running in to any performance issues caused by ballooning and swapping you may want to consider enabling TPS, which would help mitigate against both of these.