I've now experienced this issue with 3 different storage vendors, using 3 different CNA adapters (all FCoE though), so I'm fairly sure this issue is not isolated to a specific storage vendor (seen on HP 3PAR, EMC VNX and HDS G1000().
When we add a thin provisoned LUN to a host (connected via FCoE, MPIO installed) and quick format the LUN (NTFS) it takes up to 30 minutes for the format to complete. I have found other threads around that mentions this issue - but so far I've yet to find a solution/explanation. So far we've just had to live with it, but it's pretty annoying I must say. It does not appear to be related to the size of the LUN - 100GB or 2TB, it still takes 20-30mins to QUICK format the drive! That's more like SLOW format in my book.
Anyone else seeing this/have an explanation? I've seen it on Windows Server 2012 (R2) so far - not tested on 2008 (R2).