On this Alix machine, mounting root readonly after mounting it read-write is slow, as in:
% mount -w /
% time mount -r / # 15-20 seconds
A workaround is to mount the partition async in which case the remount is almost instant. My typical workflow is to mount read-write, break something, then remount read-only for the sake of fsck(8).
The original Alix series use a Compact Flash -> ATA controller. I've observed this behavior with multiple CF cards. Typical WCHAN is `biowr', `wdrain' or both. This behavior persists since at least FreeBSD 10 series.
Note, the CF storage isn't that slow, see:
cat /usr/lib/* > /dev/null 0.10s user 1.21s system 46% cpu 2.821 total
cat /usr/bin/* > /dev/null 0.12s user 3.09s system 67% cpu 4.756 total
There are some nasty things in KERNCONF, only to reduce logspam and save time otherwise spent probing for nonexistent controllers. The Alix series have none of these controllers:
nodevice xenpci # fix build
nooptions XENHVM # idem
nodevice hyperv # idem
I can attach various config files (sysctl.conf, rc.conf, dmesg.boot, fstab, KERNCONF) if necessary but they look sane other than the aforementioned KERNCONF.