On Tue, Aug 26, 2014 at 07:39:08PM -0400, Nikolai Grigoriev wrote: > Hi, > > This is not exactly a problem - I am trying to understand why BTRFS > demonstrates significantly higher throughput in my environment. > > I am observing something that I cannot explain. I am trying to come up > with a good filesystem configuration using HP P420i controller and > SSDs (Intel S3500). Out of curiosity I have tried BTRFS (still > unstable so I can't really expect to be able to use it) and noticed > that the read speed is about 150% of ext4 - while write speed is > comparable. ... > When I read, I observe different picture: > > Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util > (ext4 - reading) > sdb 0.00 0.00 4782.00 0.00 597.75 0.00 256.00 1.57 0.33 0.18 84.10 > (btrfs - reading) > Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util > sdc 207.00 0.00 1794.00 0.00 886.40 0.00 1011.90 10.59 5.90 0.56 100.00 > (xfs - reading) > Device: rrqm/s wrqm/s r/s w/s rMB/s wMB/s avgrq-sz avgqu-sz await svctm %util > sdd 0.00 0.00 4623.00 0.00 577.88 0.00 256.00 1.71 0.37 0.21 97.00 Pretty obvious difference: avgrq-sz. btrfs is doing 512k IOs, ext4 and XFS are doing is doing 128k IOs because that's the default block device readahead size. 'blockdev --setra 1024 /dev/sdd' before mounting the filesystem will probably fix it. -Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- 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
