> On Mon, Jan 04, 2010 at 11:27:48AM -0500, Chris Mason wrote:
>
>> On Fri, Dec 25, 2009 at 11:11:46AM -0500,
tytso@mit.edu wrote:
>>
>>> On Fri, Dec 25, 2009 at 02:46:31AM +0300, Evgeniy Polyakov wrote:
>>>
>>>>> [1]
http://samba.org/ftp/tridge/dbench/README
>>>>>
>>>> Was not able to resist to write a small notice, what no matter what, but
>>>> whatever benchmark is running, it _does_ show system behaviour in one
>>>> or another condition. And when system behaves rather badly, it is quite
>>>> a common comment, that benchmark was useless. But it did show that
>>>> system has a problem, even if rarely triggered one :)
>>>>
>>> If people are using benchmarks to improve file system, and a benchmark
>>> shows a problem, then trying to remedy the performance issue is a good
>>> thing to do, of course. Sometimes, though the case which is
>>> demonstrated by a poor benchmark is an extremely rare corner case that
>>> doesn't accurately reflect common real-life workloads --- and if
>>> addressing it results in a tradeoff which degrades much more common
>>> real-life situations, then that would be a bad thing.
>>>
>>> In situations where benchmarks are used competitively, it's rare that
>>> it's actually a *problem*. Instead it's much more common that a
>>> developer is trying to prove that their file system is *better* to
>>> gullible users who think that a single one-dimentional number is
>>> enough for them to chose file system X over file system Y.
>>>
>> [ Look at all this email from my vacation...sorry for the delay ]
>>
>> It's important that people take benchmarks from filesystem developers
>> with a big grain of salt, which is one reason the boxacle.net results
>> are so nice. Steve more than willing to take patches and experiment to
>> improve a given FS results, but his business is a fair representation of
>> performance and it shows.
>>
>
> Just looking at the results there, I notice that the RAID system XFS
> mailserver results dropped by an order of magnitude between
> 2.6.29-rc2 and 2.6.31. The single disk results are pretty
> much identical across the two kernels.
>
> IIRC, in 2.6.31 RAID0 started passing barriers through so I suspect
> this is the issue. However, seeing as dmesg is not collected by
> the scripts after the run and the output of the mounttab does
> not show default options, I cannot tell if this is the case.
