We have been actively migrating mailboxes to Exchange Online these last few month, over 5000 users this month alone. Some of those migrations have been self batched while others have leveraged the Microsoft FastTrack Center. This week we received a report that a number of mailboxes were stalled due to disk latency, an example of this information can be seen below.
This disk latency is occurring on the target database in one of the many Microsoft datacenters. The information I have received from FastTrack points to a problem that has been ongoing since last week and the Product Group is engaged and is slowly rolling a fix to all datacenters.
If you’ve opened a premier ticket regarding this issue be sure you work with your TAM to tag the BUG to the ticket so you are not charged for any support hours.