On 16/02/2011 17:01, Brian O'Mahony wrote:
>> I would be interested in your findings also.
Sure, but it will take a couple of weeks to finish.
> -----Original Message-----
> From: ilug-bounces at linux.ie [mailto:ilug-bounces at linux.ie] On Behalf Of Conor Wynne
> Sent: Wednesday, February 16, 2011 12:01 PM
> To: Pádraig Brady
> Cc: ilug at linux.ie> Subject: Re: [ILUG] I/O benchmarking tools
>> On 16/02/2011 11:18, Pádraig Brady wrote:
>> On 16/02/11 10:18, stephen mulcahy wrote:
>>> On 15/02/11 14:12, Conor Wynne wrote:
>>>> What tools do you guys recommend for doing some I/O benchmarking.
>>>>>>>> I've been using iozone with 20 threads, but the figures I'm getting
>>>> back are just mental. Like more than the array should be capable of....
>>>>>>>> The is the comand line I've been testing with:
>>>>>>>> /opt/iozone/bin/iozone -R -l 20 -u 20 -r 4k -s 100m -F file1 file2
>>>> file3 file4 file5 file6 file7 file8 file9 file10
>>>> file11 file12 file13 file14 file15 file16 file17 file18 file19
>>>> |tee -a /root/Test_20-threads_Iozone.txt
>>> iozone has a pretty good reputation.
>>>>>> I like bonnie++ because it has a simpler interface but afaik iozone
>>> is more accurate and more powerful.
>>>>>> if you're doing any filesystem testing, the first thing you need to
>>> be careful of is testing the performance of your os caches rather
>>> than the actual filesystem. So to be sure to be sure, you should use
>>> a test-file size that is a multiple of your system's memory size
>>> (this is certainly the case with bonnie++ and I assume the same with iozone).
>>>>>> Try that and see if it gives any improvement.
>> Re caching, since Linux 2.6.16 one can drop all cache with:
>>>> echo 1 > /proc/sys/vm/drop_caches # free pagecache echo 2 >
>> /proc/sys/vm/drop_caches # free dentries and inodes echo 3 >
>> /proc/sys/vm/drop_caches # free all of the above
>>>> Note, "dirty" stuff is not freed, so one should run `sync` first.
>>>> Coincidentally I was adding a per file cache drop to `dd` last night.
>> It will look something like:
>>>> dd if=file iflag=nocache count=0 # drop all of file from cache dd
>> if=file iflag=nocache skip=10 count=0 # drop end of file from cache dd
>> if=file iflag=nocache skip=10 count=10 # drop part of file from cache
>> dd if=file iflag=nocache of=copy oflag=nocache # copy just using
>> readahead cache
>>>> I'm wondering if I need to imply fdatasync with nocache.
>> Also perhaps conv=stream would be a useful shortcut (for the last
>> example at least).
>>>> Suggestions welcome.
> Excellent stuff, thanks to you both. Now I can settle some long running arguments over which to use, mpio or bonding for iSCSI targets... :)
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