Hey folks, I have been experimenting with btrfs on a home NAS box, and have some benchmark results that I don't believe. I'm hoping someone here has some insight on what I've missed that would cause such a result. The short version: I'm seeing roughly a 36% (on write) to 55% (on read) performance *improvement* when using btrfs on LUKS containers over btrfs on raw disks. This should not be the case! The test setup: My test file is a large file that I previously generated from /dev/urandom. I saw similar results using /dev/zero as input, as well as a repeated copy of the whole Ubuntu 14.04 ISO (i.e., real-ish data). My calculated MB/s numbers are based on the 'real' time in the output. Live-booted Ubuntu 14.04 (nightly from 3/11/14, kernel 3.13.5) 4x 4TB WD Red drives in standard (no RAID) configuration i3-4130 CPU (has AES-NI for accelerated encryption) Default BTRFS options from the disk gui, always raid10. Tested configurations: Raw: btrfs raid10 on 4x raw drives Encrypted: btrfs raid10 on 4 separate LUKS containers on 4x raw drives (default LUKS options) Read command: $ time sh -c "dd if=test.out of=/dev/null bs=4k" Raw: 5120000+0 records in 5120000+0 records out 20971520000 bytes (21 GB) copied, 149.841 s, 140 MB/s real 2m29.849s user 0m2.764s sys 0m7.064s = 133.467690809 MB/s Encrypted: $ time sh -c "dd if=test2.out of=/dev/null bs=4k" 5120000+0 records in 5120000+0 records out 20971520000 bytes (21 GB) copied, 96.6127 s, 217 MB/s real 1m36.627s user 0m3.331s sys 0m9.518s = 206.981485506 MB/s Read+Write: $ time sh -c "dd if=test2.out of=test20grand.out bs=4k && sync" Raw: 5120000+0 records in 5120000+0 records out 20971520000 bytes (21 GB) copied, 227.069 s, 92.4 MB/s real 3m49.701s user 0m2.854s sys 0m15.936s = 87.069712365 MB/s Encrypted: 5120000+0 records in 5120000+0 records out 20971520000 bytes (21 GB) copied, 167.823 s, 125 MB/s real 2m48.784s user 0m2.955s sys 0m17.956s = 118.494644042 MB/s Any ideas what could explain this result? One coworker suggested that perhaps the LUKS container was returning from 'sync' early, before actually finishing the write to disk. This would seem to violate the assumptions of the 'sync' primitive, so I have my doubts. I'm also interested in learning how I can reliably benchmark the real cost of running full-disk encryption under btrfs on my system. Thanks! Evan Powell | Technical Lead epowell@xxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
