I've been able to recreate this on a test system. The cause is clear: the bootloader decrypts only the boot drive.
My test system had /home on the second drive. And I had thought a solution would be to set the fstab(5) /home entry to include the
noauto option, then issue a bioctl(8) and mount(8) from an rc.local(5) script.
However, rc(8) still attempts and fails to mount the /home mount point. The reason is as yet unclear to me, as
noauto works fine when issuing
# mount -a or
# mount -A manually.
Removing the fstab(5) entry permits rc(8) to complete processing and pass control to rc.local(8), where bioctl(8) and mount(8) commands can be executed. You will want to test the bioctl(8) results, so that in the event of an incorrect passphrase, bioctl can be retried.
EDIT:
Here is an example rc.local(5) script that permits three attempts to enter the correct passphrase before mounting the partition.
Code:
for tries in 1 2 3; do
bioctl -c C -l /dev/sd1a softraid0
if [ $? -eq 0 ] ; then
break
fi
done
mount 5435133273012c81.a /home