Time Machine issues

Hi there,
I have a newly purchased 5N. Set it up with a 2TB share for time machine two days ago. In the past 2 days, time machine has copied only 83GB out of 400GB from my iMac to the 5N, and it’s pretty much stuck at the 83GB. Am on latest 5N firmware and am looking to back up an iMac mid-2010 running 10.11.5. 5N is connected to my home network directly via a GB switch. Thoughts as to what the issue could be?

hi joe are there any progress screens you can see about time machine, such as if time machine is showing active activity for a particular file, and at what speeds (if it shows that?)

also, is anything else using the drobo during the backups - if so, that could also be eating up bandwidth or slowing down the backup. (the same could apply to the imac possibly being used, or having a spotlight indexing, or another intensive task, which could also indirectly be slowing things down too?)

i do not have a mac, though the only other thing i can think of could be to check in dashboard (and after clicking on each drive slot to see if dashboard shows any warning or healed messages about each drive bay via the information area or dropdown) - or if you have recently modified or deleted a lot of files, then it could also be the internal drobo optimisation and space reclamation process that has slowed it down a bit.