Re: iSCSI read/write cost difference

["Julian Satran" <Julian_Satran@il.ibm.com>]

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.

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.

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       
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