Areca ARC-1280 (and ARC-1280ML’s, same product, different connector) have 24 SATA ports. But only support 16 drives in JBOD mode….or in any mode really, 16 drives exposed to the host is maximum. The controller deadlocks during POST/INIT if you have 17+ drives when it’s set to JBOD mode. So you can have 12 LUNs 2 drives each (mirrors) or some other combination of RAID, but you can’t do JBOD with 24 drives as of the most current (1.43) firmware.
I’m waiting to hear back from them exactly why this is. At least this one isn’t affecting our rollout of anything, but if there’s no “fix” for this controller it means trading out to 2×12 or 1×16+1×8 port controllers or something like that. Not a big deal for us for this operation since we plan to use Solaris ZFS which has integrated RAID with transactional support and because it’s totally integrated into the filesystem it really appeals to me as something that could be (and probably is) very reliable. They’ve also taken a lot of steps to produce a filesystem that is an order of magnitude more reliable and better at ensuring data integrity than almost anything readily available for production.