| In general this is purely default NetBSD 10.0_BETA installation. The
| only options I changed is adding log, async and noatime to / mount in
| the installer.
That's a combination that makes no sense, and I thought had been made
impossible, but you seem to have achieved it.
"async" says "just do all I/O to buffers, in any order, write to the
disc when necessary, in any order, filesystem consistency if the system
shoukd crash before umount is not guaranteed, and is often a complete
disaster". I use that a lot for trash fikesystems I can just newfs if
needed, but want to run as fast as possible - like /usr/obj. I also use
it for src/pkgsrc while unpacking as I can always newfs and start again
if something goes wrong. I'd never recommend it for root though.
"log" delays meta-data writes, but keeps track of what should be done
and in what order so the filesystem can be made consistent after a crash.
Using neither causes meta-data to be written synchronously, and in order,
so the filesystem should never become inconsistent. Safe, but slow,
particularly for things like unpacking pkgsrc, which is almost all meta-data
operations (allocating inodes, making new directory entries, ...)
Async and log are almost opposites in intent, both make the filesystem
do meta-data ops faster than the default, but in dramatically different
ways. It is possible the system is simply ignoring both of them, and
operating in safe slow mode. If not, then almost anything might be
happening internally. Just don't do that.
For root just use log. Not async. If you use a separate filesystem
for pkgsrc, you can mount that async while unpacking. That is then lots
faster. After the unpack is done, umount and mount again without async
(you can use log, or not, as you like - once unpacked, pkgsrc should
get few future changes, just perhaps occasional updates, so it doesn't
make a lot of difference - put the work directories elsewhere.)