This issue seems to be that you are doing it on an encrypted filesystem. The kernel obviously has to perform a lot of IO intermixed with computational overhead to do this.
I don't know if the performance problem is expected or not. It all depends on what encryption method you are using, etc. -- Write load on DM-Crypt LUKS partition with reiserfs jams system https://launchpad.net/bugs/82528 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
