Two SSDs if I want redundancy. Otherwise I'm in exactly the same situation as with a SATA-DOM ... which essentially is an SSD. My main question is: are these supposed to be reliable and "server grade" or rather the same consumer product quality as USB drives?
You can get industrial DOM's with good characteristics. The SLC ones will have great endurance characteristics for a boot device; many of them were designed to actually host a Windows OS and be doing "stuff."
The Supermicro ones can sustain a complete drive write per day for the 5-year warranty period. If you look at that link, you'll note that they recommend these for boot drives but not write-heavy environments.
You can also get cheap DOM's with less-good characteristics. These will be based on MLC and are somewhere between the cheap tier SSD's and carp-arse USB. The problem with all of these is that they use crappy controllers, and they don't really do proper wear leveling or other flash life-extending mitigations the way that they should. Most of those seem to have died off though.
My general impression is that the development of DOM's was heaviest back in the day before the "SSD revolution," which coincided with SLC being king. As cheap SSD and USB flash evolved, I would imagine that ate into the DOM market, and there probably isn't enough volume to justify constant re-engineering. Supermicro only recently retired the PHI series with the SMCMVN1 which is MLC.
But here's the thing, which is really the answer to your question. USB fails because USB manufacturers are under tremendous pressures to compete with their competitors, so they use the cheapest controller, the cheapest flash, the cheapest construction... which is how you sometimes find cheap USB drives on sale at the dollar store. It's *possible* to buy better-quality USB but even there, usually without the endurance characteristics you'd ideally want. SATADOM units, on the other hand, is being purchased by people who have bought an entire computing system. They probably have a significant interest in seeing that system work. Some of them have price sensitivity (think: kiosk or thin-client use) but none of them are expecting to pay $0.99 for their SATADOM (hoping, yes, expecting, no). And the people buying servers that boot from SATADOM are going to be incensed if their five figures server is rendered inoperable by the failure of a hundred dollar part.
You can buy industrial SATADOM, Supermicro's in particular, without fear.
But here's *practical* advice: avoid SATADOM's if you can, because of the cost. You can get cheap 2.5" SSD and find a place for power and to tape it inside your chassis. A modern
inexpensive 250GB Samsung (~$56) SSD will be cheaper than a 32GB SSD-DM032 SATADOM (~$60). The massively larger size means fewer write cycles, which is great for SSD. Get a second SSD, a different brand with a different controller, and you'll have a heterogeneous boot pool that is not likely to fail.
