How much space is required for client side deduplication?

Thanks for the responses.

Actually, after a lengthy discussion with support, it turned out the cause of the issue was not client side dedupe, but instead database snapshot backups of sql on the vm using the remote agent. 

So the particular vm in question resides on a datastore with very limited space, and is a dedicated sql 2008 vm.  This machine was configured with a remote agent to do file level backups, sql database backups and snapshot backups of the vm.  The file level backups appeared to be running ok, but the sql database backups running into issues, as prior to the backup, a database snapshot is taken, causing disk space usage to increase, and in turn, causing the thin disk to expand, filling up the datastore, and bringing down the vm.

Thanks again.