Perhaps I should describe what I'm seeing. I have two terminals open. In one, I launch: $ watch "ls -l foo* | head -n 20" In the other terminal I kick off fio. fio first spits out the "Laying out" messages, one per job. Immediately the full 4MB files appear in the directory listing. *Then* fio starts writing to the files, as indicated by the fio output. The size of each file never changes during the test. I wasn't expecting the full 4Mb files to be created before the sequential writes. I expected to not see any files initially, and then a file for each job growing at a rate of 200Kbs throughout the test until reaching the 4MB limit. Perhaps I'm just configuring fio incorrectly? brian On Wed, Aug 31, 2011 at 5:38 PM, Jens Axboe <axboe@xxxxxxxxx> wrote: > 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
