[Beowulf] NFS over RDMA performance confusion

Ellis H. Wilson III ellis at cse.psu.edu
Thu Sep 13 09:03:04 PDT 2012


On 09/13/2012 12:05 PM, Joe Landman wrote:
> On 09/13/2012 11:21 AM, holway at th.physik.uni-frankfurt.de wrote:
>>
>>> I assume so, but just to be clear you witnessed this behavior even with
>>> the -I (directio) parameter?
>>
>> Yes.
>>
>> for i in 1 2 4 8 16; do /cm/shared/apps/iozone/current/sbin/iozone -I -l
>> $i -u $i -r 16k -s 10M -F file1..file16 ; done>  output&
>
> -s 10M ???
>
> This is a 10M test file size.
>
> Ok.  Let me be clear, 10M as a file size is not useful as a test.  The
> numbers are, for lack of any better way to describe this, meaningless.
>
>   From the iozone man page
>
>          -s #   Used to specify the size, in Kbytes, of the file  to
> test.  One
>                 may  also  specify  -s #k  (size  in  Kbytes)  or -s #m
> (size in
>                 Mbytes) or -s #g (size in Gbytes).
>
>
> If each storage node has 128GB ram (I think this was the number) and you
> want a "serious" (as in real) test, you need to take your N storage
> nodes @128GB each, sum up the ram, double it, and that is your file
> size.  When you have that, your performance numbers will be uncached,
> and therefore far more likely to represent the actual hardware performance.

I must be filtered out by Joe's email software or something...I said 
almost verbatim this very suggestion now an hour or more ago.  :/.

Best,

ellis


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