Space reclamation has nothing to do with dedupe and compression on XtremIO. In fact, it has nothing to do with XtremIO (or any other storage).  If you delete something from the host side, you need to send a space reclamation command to the storage - some operating systems do it by default (windows) and some don't (VMware).  Because XtremIO is a content aware storage, one manual work around that will always work is writing zeroes to the deleted space. When you write zeroes from the host, XtremIO will identify it and we reclaim the storage corresponding to that area where the zero was written.
We are in the planning stages of deploying a VDI solution on XtremIO using Horizon. We have been given some conflicting information regarding space reclamation. Is it still best practice to use the VSI plugin for space reclamation or is that no longer required? Would like to see some documentation on it as the latest I can find only addresses XtremIO v3.0.   Thanks. 
VDI space reclamation on XtremIo