Re: block device benchmarking - Mailing list pgsql-performance

Markus Wanner wrote:
> Hi,
>
> I'm fiddling with a hand-made block device based benchmarking thingie,
> which I want to run random reads and writes of relatively small blocks
> (somewhat similar to databases). I'm much less interested in measuring
> throughput, but rather in latency. Besides varying block sizes, I'm also
> testing with a varying number of concurrent threads and varying
> read/write ratios. As a result, I'm interested in roughly the following
> graphs:
>
>  * (single thread) i/o latency vs. seek distance
>  * (single thread) throughput vs. (accurator) position
>  * (single thread) i/o latency vs. no of concurrent threads
>  * total requests per second + throughput vs. no of concurrent threads
>  * total requests per second + throughput vs. read/write ratio
>  * total requests per second + throughput vs. block size
>  * distribution of access times (histogram)
>
> (Of course, not all of these are relevant for all types of storages.)
>
> Does there already exist a tool giving (most of) these measures? Am I
> missing something interesting? What would you expect from a block device
> benchmarking tool?
>
> Regards
>
> Markus Wanner
>

Check out the work of Jens Axboe and Alan Brunelle, specifically the
packages "blktrace" and "fio". "blktrace" acts as a "sniffer" for I/O,
recording the path of every I/O operation through the block I/O layer.
Using another tool in the package, "btreplay/btrecord", you can
translate the captured trace into a benchmark that re-issues the I/Os.
And the third tool in the package, "btt", does statistical analysis. I
don't think you really need "benchmarks" if you can extract this kind of
detail from a real application. :)

However, if you do want to build a benchmark, "fio" is a customizable
benchmark utility. In the absence of real-world traces, you can emulate
any I/O activity pattern with "fio". "fio" is what Mark Wong's group has
been using to characterize filesystem behavior. I'm not sure where the
presentations are at the moment, but there is some of it at

http://wiki.postgresql.org/wiki/HP_ProLiant_DL380_G5_Tuning_Guide

There are also some more generic filesystem benchmarks like "iozone" and
"bonnie++". They're a good general tool for comparing filesystems and
I/O subsystems, but the other tools are more useful if you have a
specific workload, for example, a PostgreSQL application.

BTW ... I am working on my blktrace howto even as I type this. I don't
have an ETA -- that's going to depend on how long it takes me to get the
PostgreSQL benchmarks I'm using to work on my machine. But everything
will be on Github at

http://github.com/znmeb/linux_perf_viz/tree/master/blktrace-howto

as it evolves.