CPU - 2603 is basically the entry card - definitely would recommend to upgrade that - higher clock is preferred over many cores in your instance. Think 2+ (1-2 cores/user)
I think the E5-2690 v4 chips are about $300 used. That looks like the sweet spot.
Concern...Has. Was that approval or concern? budget isn't really a a concern, I just dont want to waste money for no reason.
I don't really have a true user limit in the end. At any given time I have 10 edit bays on the network via an Arista 10gbe switch. 12 spindles won't handle that stream load no matter what hardware it's backed by. I do plan to add an expansion chassis and continue to add more storage at a later date and updgrade, or replace it all with more modern server.Concern...
I said 2 (basic OS function) +1-2/user. Given you said a couple I dont see how you need a 14C/28T CPU (which operates at a medium clock level)? Dont get me wrong, its a nice CPU and a good choice if you need lots of cores (step up from the 2680 you mentioned before), but for only a couple of users? Especially if you have a dual board you can/want to use.
The 2667s @T_Minus mentioned are usually a great choice for a filer which needs a bit more single thread performance (or for low core requirements get the 16XX's, a single one runs on dual board too). You also can consider the 2687W but that might over TDP.
Also, I as well think you should spend some cash on memory .
Identify the causeWhere does one go from here?
Me too, learned the hard way.I guess I just expected mirrored vdevs to distribute more? what would happen is large chunks of data were only in 1-2 places it seems. for small files, lots of users, that would be fine. For something big, a single machine would buckle that section over the server.