use RAID5 on top of six encrypted disks /dev/sd[abcdef]
-(losetup)-> /dev/loop/[012345] -(mdadm)-> /dev/md0.
I've done this for about a year. Works just fine for me, but I'm just
a single user.
FWIW, the performance of this setup *seems* better to be better than
other things like this I've used: GEOM on FreeBSD and encrypted
loopback on top of (unencrypted) RAID5.
Anyway encrypting the disks, then aggregating those encrypted
loopback devices into a RAID5, works fine for me...