I am experiencing a very definite slowness when browsing an Exchange backup in NBU in order to perform a GRT restore for testing.
After selecting a backup image each time I attempt to drill down to a sub level it creates a new Restore task in the activity monitor and each task takes between 3 and 5 minutes to complete, during this time the restore console is unusable. For example navigating as follows "Microsoft Informaiton Store" > DB Name > Database > Mailbox name > Mailbox folder has resulted in four Restore tasks and has taken 15 minutes in order to display the contents of the inbox of a single mailbox.
At this rate it would be quicker for me to restore the entire database to a recovery database and copy the individual messages should it be required - thankfully I am just performing a test restore at the moment.
Is this slow navigation normal with NBU?
yes unfortunatelly this behaviour is normal for browsing Exchange GRT backups and VMware-based Exchange/Sharepoint GRT backups. By design GRT info for these types of backups is not catalogued at the time of backup. GRT info (so directory and file structure of mailboxes/documents) is generating just at the time of browsing - thus the longer time for this. In Activity Monitor this background work is presented as "empty" Restore job.
On the contrary, non-VMware Sharepoint GR backups are catalogued online during backups, thus browsing is much quicker.