On 2/3/2014 8:42 AM, Phillip Susi wrote: > On 2/3/2014 1:34 AM, Stan Hoeppner wrote: >> Please reread my statement above. Now let me restate that as: >> >> Measuring disk throughput when writing through the buffer cache >> isn't a measurement of disk throughput as much as it is a >> measurement of cache throughput. Thus, such measurements do not >> demonstrate actual disk throughput. >> >> Do you disagree? > > Yes, I do because cache throughput is >>>> disk throughput. It is because buffer cache throughput is greater that measurements of disk throughput are not accurate. If one issues a sync after writing through buffer cache the measured throughput should be fairly close. But without issuing a sync you're measuring buffer cache throughput. Thus, as I said previously, it is better to do parallel O_DIRECT writes or use AIO with O_DIRECT for testing disk throughput as one doesn't have to worry about these buffer cache issues. -- Stan -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
