On Fri, 2009-02-13 at 23:31 +1100, Chris Samuel wrote: > Hi folks, > > For people who might be interested, here is how btrfs performs > with two partitions on a single SSD drive in a RAID-1 mirror. > > This is on a Dell E4200 with Core 2 Duo U9300 (1.2GHz), 2GB RAM > and a Samsung SSD (128GB Thin uSATA SSD). > Thanks for posting these, it is especially good to see the metadata ops are still fast on this ssd. > Version 1.03c ------Sequential Output------ --Sequential Input- --Random- > -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks-- > Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP > sys26 2G 28299 17 18633 12 85702 29 3094 18 > ------Sequential Create------ --------Random Create-------- > -Create-- --Read--- -Delete-- -Create-- --Read--- -Delete-- > files /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP > 16 7513 99 +++++ +++ 5140 98 3964 67 +++++ +++ 5652 99 > sys26,2G,,,28299,17,18633,12,,,85702,29,3093.9,18,16,7513,99,+++++,+++,5140,98,3964,67,+++++,+++,5652,99 > So, btrfs is doing ~28MB/s writes while writing the data twice and XFS is doing 62MB writing it once. That's not too bad really. But, one important thing about the ssds is they stripe internally across a bunch of flash storage, and then they have the FTL managing all the writes. So, if you make two partitions on a single device, a raid1 data write from btrfs is very likely to result in two large IOs, which the FTL very well might put directly adjacent to each other on the SSD. Duplicating the data does make it more likely you'll recover something if the device goes bad, but two devices are still safer than one. I'm not saying the test isn't valid, I just want to make sure people reading the list don't run off and partition their ssds in hopes of getting raid ;) -chris -- 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
