Linux - Software RAID speed

Having reshaped a RAID5 twice of as many weeks, I've found that adding a 2TB drive takes a good 36 hours, which is kind of frustrating.

After a bit of searching, I discovered that there is a setting in /sys/block/md*/md/stripe_cache_size which by default is set to 256. This is enough for normal day operations, but during a reshape I was seeing speeds around 16mb/s, which meant that it would take a long time to finish.

There are mixed results, some people run into issue if they increase the value beyond 1024, other people are not seeing problems until they go to 64k. There is a performance test here which show that the optimum speed is 8192, but then again this might vary due to other issues.


linked to http://peterkieser.com/wp-content/uploads/2009/11/stripe_cache_size2.png

Try it out, it might help in your setup.

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