Fluffles wrote: > If you use dd on the raw device (meaning no UFS/VFS) there is no > read-ahead. This means that the following DD-command will give lower STR > read than the second: > > no read-ahead: > dd if=/dev/mirror/data of=/dev/null bs=1m count=1000 > read-ahead and multiple I/O queue depth: > dd if=/mounted/mirror/volume of=/dev/null bs=1m count=1000
I'd agree in theory, but bonnie++ gives WORSE results than raw device: Version 1.93c ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -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 xxxx.xxxx.xx 1G 305 99 59135 15 21350 7 501 99 57480 11 478.5 13 Latency 27325us 63238us 535ms 45347us 68125us 2393ms And pumping vfs.read_max to an obscene value doesn't really help: # sysctl vfs.read_max=256 vfs.read_max: 16 -> 256 Version 1.93c ------Sequential Output------ --Sequential Input- --Random- Concurrency 1 -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 xxxx.xxxx.xx 1G 305 99 57718 15 18758 6 500 99 60900 13 467.8 13 Latency 27325us 89977us 99594us 36706us 71907us 90021us I've experimented with increasing MAXPHYS (to 256K) before and it also doesn't help.
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