Hi Sitsofe, You wrote the following answer for a question on bad header verification back in Jan 15th of this year. I have a follow-up question on why numjobs > 1 would create interference with each other - doesn't each job write to their own file? Apologies in advance for the rudimentary question. Thanks! Albert ======= Re: FIO verify bad header question Hi, On Wed, 15 Jan 2020 at 15:32, Jens Axboe <axboe@xxxxxxxxx> wrote: > > Please use the fio list for this, CC'ed. > > On 1/15/20 8:28 AM, Michael Chichik wrote: > > > > */usr/bin/fio --time_based --runtime=1d --ioengine=libaio --iodepth=32 --rw=randrw --bs=24k --direct=0 --io_size=60G --numjobs=10 --size=1G --rwmixread=0 --verify=md5 --verify_fatal=1 --output-format=json --output=4_randrw_0_10_32_libaio_xfs_1G.json --directory /mnt/test-vol-23206-36 --name host1_test-vol-23206-36 ^^^numjobs=10 will mean all the jobs are working inside the same region. Because you're using randrw it's likely each job will write blocks in a different sequence to other jobs. > > * > > FIO failed with the following error: > > * > > * > > *verify: bad header rand_seed 1089408830752521594, wanted 7280637923435198810 at file /mnt/test-vol-23206-36/filename offset 776945664, length 24576 This means job 2 can interfere with the writes of job 1 so when job one comes to do a verify it can't find the blocks written by itself (because it may find job 2's data). If you're going to use numjobs I'd strongly look into use offset_increment (https://fio.readthedocs.io/en/latest/fio_man.html#cmdoption-arg-offset-increment ) and size (https://fio.readthedocs.io/en/latest/fio_man.html#cmdoption-arg-size ) to ensure each job is working within a different region to any other job.
