Benchmarking some stuff:
Plain (RAW partition)
root@mono:/etc# time dd if=/dev/urandom of=/dev/sda1 bs=1M count=100 100+0 records in 100+0 records out 104857600 bytes (105 MB) copied, 25.584 s, 4.1 MB/s real 0m25.589s user 0m0.004s sys 0m25.462s
Blowfish cipher
root@mono:/etc# time dd if=/dev/urandom of=/dev/mapper/swap bs=1M count=100 100+0 records in 100+0 records out 104857600 bytes (105 MB) copied, 28.8699 s, 3.6 MB/s real 0m28.876s user 0m0.000s sys 0m25.918s
AES-256 cipher
/dev/mapper/swap is active: cipher: aes-cbc-plain keysize: 256 bits device: /dev/sda1 offset: 0 sectors size: 4000122 sectors mode: read/write root@mono:/etc# time dd if=/dev/urandom of=/dev/mapper/swap bs=1M count=100 100+0 records in 100+0 records out 104857600 bytes (105 MB) copied, 29.0696 s, 3.6 MB/s real 0m29.076s user 0m0.004s sys 0m25.722s