Have you tried the Pogoplug Series 4 with the SATA port on top with NetBSD? What version?
Yes. The only change needed to netbsd-7 to make the PogoPlug v4 work properly is this:
http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/dev/marvell/mvsdioreg.h.diff?r1=1.1&r2=1.2&only_with_tag=MAIN The kernel configuration file is in -current but can also be fetched here: http://ftp.netbsd.org/pub/NetBSD/misc/jklos/POGO To make the whole process easier, you can use this: https://hackaday.io/project/407-install-netbsd-on-a-pogoplugI need to update that project a little, but mostly for details that don't affect following the article. For instance, the pre-built kernel is from netbsd-7 and has npf, not ipfilter, which is worth mentioning.
With a Samsung SSD, I get 166 MB/sec with straight dd. The USB 3 ports seem to wok fine (with a little more diagnostic output in dmesg than usual), but I don't have any USB 3 devices, so I've only tested with USB 2.
John