On one of my SQL servers we've been having really slow login issues. The server will be running ok if we don't log into it after a restart. But every time we try to login after a server restart, the whole server will be freezing up for a long time, last time I watched it took 3 hours for the server to back to normal. During this time the server only responds to ping command and no one can connect to the SQL databases. We couldn't figure out why until today: The server has got close to 30 thousand phantom drives from the Nimble snapshot(we snapshot every hour). And the server will try to enumerate all of them upon a user's login after a reboot. That's why it takes that long before the server can go back to normal. So it turns out that each time a snapshot is taken it will create a disk drive on the server, and then it becomes orphaned and stays as a phantom drive on the server. The nimble toolkit does have registry settings to clean the phantom devices automatically but by default it is disabled. So now I'm cleaning up those phantom drives manually and it will take me a full day to finish it.
You can find the information about the registry settings in this link:
After learned it the hard way I figured I'll share with everyone here so you don't run into this problem like I did.