On 2011-08-31 15:21, Jens Axboe wrote: >> I also have another (maybe related?) question. Apologies if this >> belongs in a separate thread, but are there any notes explaining why >> fio lays out the files before starting sequential writes? The >> workload I was hoping to simulate is sustained, sequential writes to >> disk. I'm trying to answer the question "How many simultaneous >> 200kBps writers can we support?" Using my current jobs file, fio >> starts by creating the files (e.g "foo0: Laying out IO file(s) (1 >> file(s) / 4MB)") before it starts processing. However, creating the >> files in advance accounts for a chunk of performance that doesn't seem >> to be measured by fio. Am I misunderstanding how to configure fio or >> its intended usage? > > You should be able to set overwrite=0 to avoid that. Are they random > writes? overwrite=0 is even default. I'm thinking the "Laying out IO file" message is confusing, it wont actually write contents first unless you ask it to (with eg overwrite=1). -- Jens Axboe -- 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
