Hi, On Wed, 25 Dec 2019 at 09:12, Oleg Sivokon <oleg.sivokon@xxxxxxxxx> wrote: > > Hello list, > > I'm wondering how the configuration below is interpreted: > > [global] > ioengine=libaio > direct=1 > loops=1 > numjobs=8 > > [write-prep] > rw=write > filename=/dev/sdb > iodepth=16 > bs=16k > fill_device=1 > stonewall=1 > > Will every one of the 8 jobs try to fill the device completely or will Yes the device will be filled but not due to fill_device=1. Confusingly fill_device is actually meant for when you are creating files on filesystems where you want the file to use up all the remaining space (https://fio.readthedocs.io/en/latest/fio_doc.html#cmdoption-arg-fill-device says this a different way). A file representing a device will already have a fixed size that can't be grown by just writing to it (OK there's thin provisioning but even there the "device" has a fixed size ahead of time). When a file already has a size that is what is used when "size" is not set (see https://fio.readthedocs.io/en/latest/fio_man.html#cmdoption-arg-size ). > they split the task of filling the device between themselves, where each > will do only 1/8 of filling the device? My reading of documentation No they will all overwrite/overlap the same areas. > seems to suggest the device will be filled 8 times, with jobs, possibly, > stepping on each other's toes (i.e. contesting the same block), but I'm > not sure. Your reading is correct - they will step on each others toes. If you want to somehow avoid this you'll have to look into 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 ). NB: stonewall=1 likely won't do anything in this case because no job definition is "after" another when using numjobs within the same job. -- Sitsofe | http://sucs.org/~sits/
