Transparent Page Sharing (TPS) is a mechanism used by the VMkernel for more effective use of physical memory resources by only storing once memory pages that are identical on two or more virtual machines. Each virtual machine has only read access to shared memory pages, and as soon as a virtual machine tries to modify a shared page, a new private copy is created by the VMkernel.

Shared pages are most commonly seen when a host is running multiple virtual machines with the same guest operating system. However, the advent of more and more x64-based guest operating systems, where the guest leverages large page tables, has seen the effective benefits of TPS being significantly reduced.

More recently however, prompted by academic research in 2014 that leveraged TPS to gain unauthorized access to data under certain highly-controlled conditions, changes to the default TPS settings in the ESXi update releases of Q4 2014 and Q1 2015 were made.

Although VMware believes the risk of TPS being used to gather sensitive information is low, so that ESXi ships with default settings that are as secure as possible, TPS management options have been introduced and inter-virtual machine TPS is no longer enabled by default. Administrators are able to easily revert this new default behavior to enable TPS if they want to do so.

For more information with regard to TPS security and any concern you might have, refer to the following knowledge base articles: