I’m in the process of converting my Fedora/rawhide laptop to Debian.
On Fedora the AES encrypted filesystems deliver about 38MB/s read speed according to dd. On Debian the speed is 2.4MB/s when running Xen and 2.7MB/s when not running Xen. The tests were done on the same block device.
Debian uses a SMP kernel (there are no non-SMP kernels in Debian), but I don’t expect this to give an order of magnitude performance drop. Both systems use i686 optimised kernels.
Update: As suggested I replaced the aes module with the aes_586 module. Unfortunately it made no apparent difference.
Update2: As suggested by a comment I checked the drive settings with hdparm and discovered that my hard drive was not using DMA. After I configured the initramfs to load the piix driver first it all started working correctly. Thanks for all the suggestions, I’ll post some benchmarks of encryption performance in a future blog entry.