[nycbug-talk] Measuring Disk Performance

Edward Capriolo edlinuxguru at gmail.com
Thu Dec 15 10:50:52 EST 2011

Unless you are using a very specific application DD does not prove much. DD
is doing linear writes which are very fast even with low RPM sata. If you
are benchmarking a disk you are likely doing it for a database. Database
workload are usually more seeking then streaming. That was one of the
reasons why I mentioned YCSB even though it is not a traditional disk tool.
You can create a solid amount of random data and read it back with
distributions like zipfan, latest, or random. This gets your disks seeking
and shows how they perform under some load. Another way to go is use the
TPH-C relational database type benchmarks, because they represent a real
world type workload. But iozone makes the nicest graphs for sure :)


On Thu, Dec 15, 2011 at 10:12 AM, Jesse Callaway <bonsaime at gmail.com> wrote:

> the advantage to some of the heavier tools is that they attempt to break
> caching mechanisms so that you can see worst case performance.
> dd looks cool since it certainly skips any possibility of filesystem
> speedups.
> I'd just say to make sure 1G (or whatever you test with) is large enough
> to break controller and on-disk cache.
> On Dec 15, 2011 9:21 AM, "Isaac Levy" <ike at blackskyresearch.net> wrote:
>> On Dec 15, 2011, at 12:54 AM, Henry M wrote:
>> Whenever I've bench-marked disks, I've always just used dd and /dev/zero
>>  Example: I want to see how fast I can write a 1GB file
>> $ dd if=/dev/zero of=1GB bs=1024 count=1048576
>> 1048576+0 records in
>> 1048576+0 records out
>> 1073741824 bytes (1.1 GB) copied, 8.72947 s, 123 MB/s
>> As long as the system load is consistent, you should get consistent
>> results. You can have fun by running multiple versions at once, to simulate
>> heavier "real-world" load.
>> Oh- &, a little xargs, and some date(1) and time(1) fun.
>> You can change the byte size, or count accordingly. Just be careful what
>> values you give dd, you can easily fill up your disk, or break something
>> nasty with a typo (Yes I've done both )
>> -Henry
>> Yeaaahhhh- this is exactly what I was thinking, but I didn't think to
>> just dd from /dev/zero and build some small tests.
>> Sweet.
>> Rocket-
>> .ike
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