I received this question a couple of times and there’s no real definitive answer written anywhere…
“Does storage vmotion require additional disk space on the source volume?”
The answer is: Yes it does. Storage VMotion uses the snapshot technology to release the lock on the source disk. This snapshot is placed on the source volume. So in other words, all changes that take place during a Storage VMotion are written to the delta file. This delta file, can and will grow fast.
So keep this in mind if you need to storage vmotion a VM because the VMFS volume is running out of diskspace… it might run out of diskspace sooner than you think.