Since the goal of this little project is to actually read my geli-encrypted zfs filesystems on a Linux laptop, I had to get a USB enclosure that supports drives bigger than 2TB; I also got a model which supports USB 3.0. The news I have is:
Ungeli and zfs-on-linux work for this task. I was able to read files and verify that their content was the same as on the Debian kFreeBSD system.
The raw disk I tested with (WDC WD30 EZRX-00DC0B0) gets ~155MiB/s at the start, ~120MiB at the middle, and ~75MiB/s at the end of the first partition according to zcav. Even though ungeli has had no serious attempt at optimization, it achieves over 90% of this read rate when zcav is run on /dev/nbd0 instead of /dev/sdb1, up to 150MiB/s at the start of the device while consuming about 50%CPU.
(My CPU does have AES instructions but I don't know for certain whether my OpenSSL uses them the way I've written the software. I do use the envelope functions, so I expect that it will. "openssl speed -evp aes-128-xts" gets over 2GB/s on 1024- and 8192-byte blocks)
Unfortunately, zfs read speeds are not that hot. Running md5sum on 2500 files totalling 2GB proceeded at an average of less than 35MB/s. I don't have a figure for this specific device when it's attached to (k)FreeBSD via sata, but I did note that the same disk scrubs at 90MB/s. On the other hand, doing a similar test on my kFreeBSD machine (but on the raidz pool I have handy, not a volume made from a single disk) I also md5sum at about 35MB/s, so maybe this is simply what zfs performance is.
All in all, I'm simply happy to know that I can now read my backups on either Linux or (k)FreeBSD.
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