Did you ever wonder why presizing your databases takes so long? At least I did - being the non-DBA that I am. The reason why is that instant file initialization is not turned on by default. Paul S. Randal summarizes the ins & outs of this process on his blog. 

If you don't run your SQL server with a service account that is local administrator (of course you don't), than you have to grant your SQL service account the "SE_MANAGE_VOLUME_NAME" permission. This can be done through the Local Security Settings of your server. Be aware that it doesn't work for log files though...