Write speeds (4 tests):
- 1 GB (from /dev/zero) write to non-FileVault space: 16.43s, 15.97s (about 60 MB/s)
- 1 GB (from /dev/zero) write to FileVault space: 39.18s, 39.03s (about 28 MB/s)
- 1 GB read from non-FileVault, write to non-FileVault: 16.52s, 14.60s
- 1 GB read from FileVault, write to non-FileVault: 16.32s, 14.25s
- 1 GB read from FileVault, write to FileVault: 36.3s, 35.41s
It's possible that disk caching might be affecting the results -- anybody know how to tell??
Bottom line:It looks like there's a nearly-2.5x penalty in write speeds when writing to a FileVault-ed account, 27 megabytes/sec vs. 60 megabytes/sec. You do pay a price for some peace of mind. On the plus side the read speeds appear to be about the same.
Don't forget, if there's a chance someone's going to walk off with your machine, make sure you power it down. =)