We're probably going to need new Linux iSCSI target software
When I think ahead to our theoretical 2018 fileserver refresh, one of my thoughts is that we're probably going to need new iSCSI target software. We're currently using IET and while we like it and there's is nothing deeply wrong with it I have to admit that it lacks some moderately important features and the pace of its development is what could politely be called 'quiet'. In fact it's sufficiently quiet that I don't know if IET will be adapted to future Linux kernels, and by 2018 even 'enterprise' long term support distros will likely be using future kernels.
If we're going to change iSCSI target software the obvious choice is the LIO target, which is the current in-kernel implementation and hopefully also the future one (the kernel changed implementations once already). There are other alternatives (the ArchLinux wiki has a decent overview), but none of them seem compelling enough to go outside the standard kernel and thus what Linux distributions will package the tools for and support as (relatively) standard.
(On the flipside, I haven't conducted any sort of deep evaluation of the other options. I wasn't impressed with anything apart from IET in my original evaluation, but that was years ago.)
I've looked into LIO some and I can't say I'm terribly enthused, for two reasons. LIO configuration is rather complicated, and it really wants to be done through a command line tool instead of a configuration file (and an interactive one at that); the latter is a bad flaw that I've written about before. LIO's tool save the resulting live configuration in JSON file(s) and in theory you can create the file yourself by hand. LIO also has a Python API, rtslib, so another option would be to create our own program to set up the iSCSI target configuration (either once or on boot) from a simpler file format.
At some point I'm going to need to test and experiment with LIO. However I don't know if it's worthwhile to do it just yet as opposed to about two years from now, since a lot can change in that sort of time.
(In a way, worrying about specific software is silly at this point. Things in the open source world can change drastically over two years and anyways there are any number of things that are up in the air about a future fileserver design. I just think about this now because I've wound up thinking that IET is getting long in the tooth and kind of neglected by now, so we're going to have to do something about it sooner or later.)