Hi, On 27 December 2016 at 04:33, Saju Nair <saju.mad.nair@xxxxxxxxx> wrote: > > > Re verification speed: When you say the speed is one tenth that of > > regular reads are the "regular" reads also using numjobs=1? If not the > > comparison isn't fair and you need to rerun it with numjobs=1 > > everywhere and tell us what the difference was for those runs. > > Yes, it was with num_jobs = 1 in both cases of "regular read" and "read-verify". I think it is understandable that there is a performance drop, since the compare/verify is done on-the-fly.. Where does FIO store the data read, before the verify step is executed. During a verifying read the data of the block read is kept in RAM and if needed (depends on the verification type) the data to compare against is regenerated. Because of this very little or no data needs to be stored during the write phase. One option to try and speed verification up (assuming you have the spare CPUs) could be to use verify_async (see the HOWTO). Another option could be to use faster verification comparisons (see verify=str of the HOWTO). For example the verify=crc32c checksum calculation will be hardware accelerated on recent x86 machines. Do either of these make a difference? -- Sitsofe | http://sucs.org/~sits/ -- To unsubscribe from this list: send the line "unsubscribe fio" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
