Fixed; the MTU setting on my storage switch was clipping some of the storage traffic. Below are the troubleshooting steps that I went through, maybe it'll help someone else out. The solution didn't exactly have anything specific to do with ESXi or EqualLogic. Basic troubleshooting and digging.
Inspection of the storage array logs/events indicated it saw and accepted the ESXi host connection appempts. I saw messages to the effect of:
- Connection from ESXi iqn bla bla bla established; CHAP authentication successful.
- 10 secs later: Connection reset/aborted by peer.
- 5 secs later: Connection from ESXi established successfully....
(rinse and repeat several times over)
Inspection of the ESXi hostd.log file shown several 'connection reset by peer' messages. Both the storage array and ESXi were pointing at each other.... and the switch is the only thing in the middle.
Troubleshooting steps now:
- using vmkping to ping the array from the ESXi - successful: vmkping 192.168.1.20
- using vmkping to ping the array from the ESXi with a size of 9000 (jumbo frame size): NO RESPONSE!: vmkping -s 9000 192.168.100.20 (<-- this is where the money was for finding the issue)
MTU was set to 9000 everywhere. Turns out the switch needed to be set a little higher (to account for packet headers??? who knew 
)
So, this setup ran for over a year untouched working and just stopped when we took it all down and brought it back up. 