Re: iSCSI read/write cost difference

[mingz <mingz@ele.uri.edu>]

On Friday 18 April 2003 03:36, Julian Satran wrote:
> For UNH code you have to address UNH. I suspect they do not incorporate
> the status in the last data and that slows write.
> For large data sizes on write you may also be slowed down by the target
> not issuing R2Ts in time. The jump should be visible when you start
> needing R2T.
Thx so much. this is why I contact David Woolf. Hi David, u come from UNH IOL 
right?


>
> A high performance target will issue the required R2T as soon as it has
> the command while a test target migh be more "relaxed".
>
> Some tcp traces may help you - but please don't send them to me - that was
> a suggestion for you to analyze.
> TCP traces contain timestamps.
I will do this, thx. 

>
> Julo
>
>
>
> mingz <mingz@ele.uri.edu>
> Sent by: owner-ips@ece.cmu.edu
> 18/04/03 05:48
> Please respond to
> mingz@ele.uri.edu
>
>
> To
> David Woolf <djwoolf@io.iol.unh.edu>
> cc
> ips@ece.cmu.edu
> Subject
> Re: iSCSI read/write cost difference
>
>
>
>
>
>
> yes, i test these three situations and get the results as follows
>
> 1) for all InitialR2T =Y/N, ImmediateData = Y/N, the read results are all
>  same.
> 2) initialr2t has no influence on write
> 3) immediatedata has influence on write.
>
> IOPS: (scsi ram disk)
>                                  2k                              4k   8k
>                  16k                             32k
> read                             1975            1781            1557
> 1081             767
> write            2877            2225            1588            812   533
> (immediatedata =yes)
> write            1971            1527            1199            880   566
> (immediatedata =no)
>
> when immediaredata=yes,  for small write, data go with the command, so
> should
> be faster, but why with large data size, like 16k and 32k, the write is
> slower? and why write is always slower than read with large data size?
>
> btw, can u answer this question,  'Also, does the target piggyback SCSI
> Response in the Final Datain pdu?' since this code is from your unh iol,
> hehe. thx.
>
> On Thursday 17 April 2003 14:19, you wrote:
> > Hello,
> > Have you done these experiments with InitialR2T=Yes and
>
> Immediatedata=No,
>
> > InitialR2T=Yes and Immediatedata=Yes, and InitialR2T=No and
> > ImmediateData=Yes? I'd be interested to see how the results change.
> >
> > thanks,
> >
> > David Woolf
> > ************************************************
> > University of New Hampshire Interoperability Lab
> > iSCSI and Fibre Channel Consortiums
> > Durham, NH 03824
> > (603) 862 0701
> > ************************************************
> >
> > On Thu, 17 Apr 2003, mingz wrote:
> > > I recently did some experiments on iSCSI benchmarking. I used the UNH
> > > iSCSi ref18_03 implementation and use a ram based scsi device for
>
> iscsi
>
> > > target use. so there is no any disk overhead.
> > >
> > > I used a linux kernel module to send fixed size read/write requests to
> > > iscsi initiator, which eventually will be filled by iscsi target. i
>
> use
>
> > > interl pro1000 gigabit nic and intel 470 gigabit switch. and both
> > > initiator and target use same type piii 866 pc with 1g ram.
> > >
> > > now the IOPS result shows that
> > >
> > >                              2k                              4k   8k
>
>                  16k                             32k
>
> > > read                                 1975            1781 1557  1081
>
> 767
>
> > > write                2877            2225            1588 812   533
> > >
> > > for small reuqests, read is slower than write, while for large
>
> requests,
>
> > > read is faster than write. i redo the experiments on another
>
> enviroment,
>
> > > also get similar results.
> > >
> > > can anybody explain why this happens?
> > >
> > > thanks a lot.
> > >
> > >
> > > ming

-- 
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| Ming Zhang, PhD. Student                                     
| Dept. of Electrical & Computer Engineering       
| College of Engineering                           
| University of Rhode Island                       
| Kingston RI. 02881                                  
| e-mail: mingz@ele.uri.edu                        
| Tel. (401) 874-2293 Fax  (401) 782-6422          
| http://www.ele.uri.edu/~mingz                     
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