The parameters are set in files located at:
For example, the parameter read_expire on a device hda is stored in:
The parameter can be set to 80 (milliseconds) using the command:
echo 80 > /sys/block/hda/queue/iosched/read_expire
This has five tunable parameters:
In addition to read_expire and write_expire, the anticipatory scheduler also includes:
Although there are no hard and fast rules, a sensible strategy is probably to benchmark I/O using different schedulers with their default parameter settings, and then to choose the most appropriate scheduler and attempt to fine-tune the parameter settings by referring to application-specific recommendations.
Don't forget that scheduling isn't the be all and end all of I/O optimization. Other factors that can affect performance include prefetching, disk capacity and spin rate (because these can affect seek time) and even the file system you choose for a given disk. One thing is certain: Whatever performance you are getting now, you can almost certainly improve it if you have the time, the will and the knowledge.
Paul Rubens is an IT consultant and journalist based in Marlow on Thames, England. He has been programming, tinkering and generally sitting in front of computer screens since his first encounter with a DEC PDP-11 in 1979.Article courtesy of ServerWatch
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