Thursday, 24 September 2009

Using the noop I/O scheduler

Over the past few days I've been tweaking the configuration on my HP Mini 1000 to see how to squeeze a little more performance out of this device. Today I enabled the NOOP I/O scheduler on the SSD as this improves performance a little.

Since the SSD is just a flash memory based device, it has minimal seek time and zero rotational delay, so it's sensible to disable the more complex default cfq I/O scheduler and just use the simpler NOOP scheduler. The NOOP scheduler just puts all I/O requests into an unordered First-In First Out (FIFO) queue, and can also do request merging. The rationale behind this is that I/O performance optimisation is performed by the block device such as the logic in the SSD controller.

Traditional hard disks have the overhead of head movement seek times and also rotational delay and it makes sense for these devices to try and group I/O requests together if they are physically close on the disk. However, with SSDs this does not make sense as these delays don't apply - the NOOP I/O scheduler is a better choice as it removes the grouping of I/O requests and hopefully reduces the variability in timing of I/O request completion.

To enable the NOOP I/O scheduler on SDD device /dev/sda, I used (as root):

echo noop > /sys/block/sda/queue/scheduler

..and of course this should be placed in the appropriate boot scripts.


  1. What about write magnification? The write magnification will bite into your performance much more and also increase wear and tear of the NAND memory.

  2. @towolf, what kind of write magnification does one get with NOOP over the other I/O schedulers? Any data or reference material I can look at? Thanks! Colin.