Hi, we would like to write a testplan to benchmark our ceph cluster. We want to use fio for it. According to an article from Sebastian Han [1] ceph is using libaio with O_DIRECT for writing data to the journal. In a different blog article [2] I read that ceph is using D_SYNC as well for this. This basically means it is using a queue depth of 1 (issue one IO request and wait for it to be done), right? Testing this with fio can be done by using the params direct=1 and iodepth=1 with engine=libaio. After this the journal gets flushed to the OSD disk. This time buffered IO is used (in fio terms: direct=0). My question is: Which iodepth is used for this (so which value to use in fio)? In the source code of ceph I can see that the io_setup() function gets called with '128' concurrent events available. So should I use iodepth=128 in fio for this? Maybe I do have a wrong understanding of async IO as well :-) Thanks for any clarification of this topic Cheers Nick [1] https://www.sebastien-han.fr/blog/2013/10/03/quick-analysis-of-the-ceph-io-layer [2] http://bryanapperson.com/blog/ceph-raw-disk-performance-testing/ -- Sebastian Nickel Nine Internet Solutions AG, Albisriederstr. 243a, CH-8047 Zuerich Tel +41 44 637 40 00 | Support +41 44 637 40 40 | www.nine.ch
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