Block devices are important to host performance. Correct configuration of the block device queue depth, scheduling algorithm, prefetch amount, and I/O alignment improves system performance.
Scheduling Algorithm
Linux 2.6 kernel supports four types of block device scheduling algorithms: noop, anticipatory, deadline, and cfq. The default scheduling algorithm is cfq. To query the block device scheduling algorithm in use, run cat.
linux-ob3a:~ # cat /sys/block/sdc/queue/scheduler
noop deadline [cfq]
Inappropriate configuration of the scheduling algorithm affects system performance, such as I/O concurrency. You can use the following method to temporarily change the scheduling algorithm of the block device:
echo noop > /sys/block/sdc/queue/scheduler
NOTE
You can tune the performance by temporarily changing the queue depth of a block device. After the application server is restarted, the queue depth is restored to the default value.
