In vSphere 5.5 and 6.0 a new command was given to esxcli. With this command you can reclaim deleted blocks on thin-provisoned LUNs.
You could run the mechanism in production time. This might sound good…. Our maintainance windows gets smaller and smaller with every new service and if you could do maintainance when everybody could work is that great.
BUT one moment!
The ESXi host which runs the reclaim would get very high cpu usage and might costops VMs within the host. Especially the first run will take a lot of time.