Running ZFS With CAM-based ATA On FreeBSD 8.1

With simple 64MB and 256MB reads of 16 counts, the CAM-based infrastructure slowed things down here too.

While there will be more interesting data to look at later this week when the FreeBSD file-systems are compared to EXT4 and Btrfs on Linux, the tests today show that the CAM-based ATA infrastructure being introduced in FreeBSD can show some modest gains (up to 30~40%+) under some I/O workloads namely with PostMark, and continuous writes even with multiple threads. In other tests the benefits were much more humble at around 8%. However, with our test system, the random writes and even the reads had regressed compared to their existing ATA infrastructure. It's a bit concerning to see the CAM-based ATA infrastructure being more than three times slower with some of these regressed tests. While CAM may have improved a lot between FreeBSD 8.0 when it was introduced and the newest FreeBSD 8.1 release, it looks like there still is some optimization work ahead and hopefully by the time FreeBSD 8.2 rolls around it will be in better condition to be enabled by default. Again, the CAM-based ATA infrastructure also adds other features to FreeBSD like NCQ support for SATA devices and better hot-plugging.