Objects, components, and witnesses
Earlier, we simply stated that the reads/writes are targeted to the virtual disk associated to the guest operating system or VM, while in the conventional VMFS filesystem this is fairly straightforward, as a virtual disk(s) relates to the set of VMDK files.
While this is similar in Virtual SAN from an administrator's perspective, under the covers the mechanism significantly varies. This is because there is a newer set of challenges to be dealt with by VSAN from a software-defined storage perspective. Some of the challenges are policy-based provisioning (availability and performance) and vSphere features that are dependent on shared storage.
These are particularly challenging given that virtual machine data is now confined to local storage.
To address these challenges, VSAN uses a VMFS-derived filesystem called VMFS-L, which is an object-based storage system where objects are distributed across the cluster based on a distributed RAID concept.
