Ultra 6 won't boot after erase

[waldhaus1]

I just got an ultra 6. I put one Hitachi 3tb drive in and it seemed to work ok. I then added 2 more and it reported only 976 gb of space available. It seemed a reformat might be in order. I tried the factory default reboot and selected erase. That took about 11 hours, following which the unit shut down. When I restart it hangs on the Ready NAS screen and doesn't boot. If I remove the drives it boots OK.
Do the disks need a low level format now? Will the Ultra do that?
I can't tell if the unit is doing anything when I power it on with one of the disks in it. (The disk does seem to spin up.)

[mdgm-ntgr]

Sounds like one disk is bad. Please confirm which one.

Try factory reset with one disk installed.
Update to 4.2.16 via System > Update
Then update to latest firmware

4.2.16 adds GPT support. This is necessary to see the full capacity of 3TB disks. On 4.2.15 or earlier < 1TB is recognized.