Our problem with OmniOS upgrades: we'll probably never do any more
Our current fileserver infrastructure is currently running OmniOS r151014, and I have recently crystallized the realization that we will probably not upgrade it to a newer version of OmniOS over the remaining lifetime of this generation of server hardware (which I optimistically project to be another two to three years). This is kind of a problem for a number of reasons (and yes, beyond the obvious), but my pessimistic view right now is that it's an essentially intractable one for us.
The core issue with upgrades for us is that in practice they are extremely risky. Our fileservers are a core and highly visible service in our environment; downtime or problems on even a single production fileserver directly impacts the ability of people here to get their work done. And we can't even come close to completely testing a new fileserver outside of production. Over and over, we have only found problems (sometimes serious ones) under our real and highly unpredictable production load.
(We can do plenty of fileserver testing outside of production and we do, but testing can't show that production fileservers will be problem free, it can only find (some) problems before production.)
Since upgrades are risky, we need fairly strong reasons to do them. When our existing fileservers are working reasonably well, it's not clear where such strong reasons would come from (barring a few freak events, like a major ixgbe improvement, or the discovery of catastrophic bugs in ZFS or NFS service or the like). On the one hand this is a testimony to OmniOS's current usefulness, but on the other hand, well.
I don't have any answers to this. There probably really aren't any, and I'm wishing for a magic solution to my problems. Sometimes that's just how it goes.
(I'm assuming for the moment that we could do OmniOS version upgrades through new boot environments. We might not be able to, for various reasons (we couldn't last time), in which case the upgrade problem gets worse. Actual system reinstalls, hardware swaps, or other long-downtime operations crank the difficulty of selling upgrades up even more. Our round of upgrades to OmniOS r151014 took about six months from the first server to the last server, for a whole collection of reasons including not wanting to do all servers at once in case of problems.)