Yes indeed, whilst you convert, you can resize the target disks but hey, as Rick Vanover experimented, it is twice as slow as doing a regular block level copy. Why? because when resizing the target disk, vConverter switches to file level copy and it’s really slow…
Now what’s the trick? The issue with the faster process is that there is potentially large amounts of wasted space on the SAN. This can be solved by vSphere’s Enhanced Storage VMotion. The enhancements in vSphere allow you to perform a storage migration task from a fully allocated virtual disk to a thin-provisioned disk. This means that once the workload is converted, you can perform this task to reclaim that wasted space. This is a timesaver, as the Storage VMotion task is done online with the virtual machine. The only caveat is that there needs to be enough space on the storage platform to support all of the pieces in motion, which may add up if there is a lot of free space involved.
Thanks Rick for the trick!