Re: Running a separate fio process for each disk?

[Jens Axboe <axboe@kernel.dk>]

On 11/20/2015 12:37 PM, Caio Villela wrote:
> Hello Allen and Jens,
>
> Sorry for the long output, this is just in case you want the details.
> Here is a simple explanation for the problem. I want to run a 15 minute
> random write, using 1 Meg requests, and measure throughput and latency.
> What seems to be the problem is that if the test system has a large
> number of drives - the system that I am testing here has 28 drives -
> then the time accounting seems to go bad for some of the processes.
> What you see below is that during the 15 minutes from start, all disks
> are getting hit the same, as they should. Then, after 15 minutes, there
> are 15 drives that are still running.... after 5 minutes over the
> specified 15 minutes, there is still one drive running. Then looking at
> the amount of IOs sent to each drive, the ones that ran on that excess
> time have much more IOs. FIO still reports that all drives ran for 15
> minutes, although some ran for more than 20 minutes.
>
> We will attempt to run a single process instead of 28 instances of FIO
> to see if this goes away.

Could you also check if adding clocksource=gettimeofday makes any 
difference? This sounds very odd.

Assuming this was run with fio -git?

-- 
Jens Axboe