Hi, On Wed, 29 Apr 2020 at 04:39, Hamilton Tobon Mosquera <htobonm@xxxxxxxxxxxx> wrote: > > Hi there, > > I'm trying to run some benchmarks using the ioegnines libaio and > pvsync2. I'm trying to run sequential reads/writes and random > read/writes in a file of 200G with a maximum of 4 jobs, that is, > threads. I don't mix them, that is, I run sequentially or randomly > reads/writes. > > My question is this: when running sequentially, given that I'm using 4 > threads, is it really sequential?. Do the threads interfere with each > other?, if yes, which options should I use to make each thread only Sequential to which layer? It's worth noting that the more concurrent sequential streams there are the more a workload will appear to be random to the lower levels. From an fio perspective without seeing the actual job it's hard to answer your question. For example, if each of the four sequential jobs are working on the same file (because you specified filename) then there's a high chance of interference and it's hard to say what the interference will look like given the interaction of the cache etc. If they are separate files then I guess you would argue they don't interfere... > issue requests to disjoint parts of the file, each of 50G (in case of 4 > threads). I tried using offset_increment, but sometimes it overflows on > random requests, and for sequential requests the file size increases > automatically, that is, the requests are going further the size of the > file, but it does not crashes. More specifically, I get the file size in > bytes, exactly 214748364800. I divide that number in the number of > threads, and I use the result as the offset_increment. The file is > created using the filecreate engine with size 200G. In your case I would expect you would have to use offset AND size to limit the region worked within (see https://fio.readthedocs.io/en/latest/fio_doc.html#cmdoption-arg-offset ). > Lastly, is it possible for each thread to issue random requests only in > that piece of 50G, so that it does not overflows to other threads piece > of file or even overflow outside the file?. See above! -- Sitsofe | http://sucs.org/~sits/
