All streams have a buffer associated with them (SIZE_DATA_BUFFERS and
NUMBER_DATA_BUFFERS).

The streams fill the buffers.  When a buffer is full, it goes to tape.  

Watch your bptm logs and it will show you how long it takes to fill the
buffer (waited for full buffer). 

If you look at the requirements for determining the BUFFERS size, you will
see MPX in the formula.

The slower clients fill the buffers at a slower rate.

The higher the number of MPX, the longer it takes to check/empty the
buffers.




Bobby Williams
2205 Peterson Drive
Chattanooga, Tennessee  37421
423-296-8200

-----Original Message-----
From: veritas-bu-bounces AT mailman.eng.auburn DOT edu
[mailto:veritas-bu-bounces AT mailman.eng.auburn DOT edu] On Behalf Of Justin
Piszcz
Sent: Thursday, September 06, 2007 7:19 AM
To: Clooney, David
Cc: veritas-bu AT mailman.eng.auburn DOT edu
Subject: Re: [Veritas-bu] MPX Explanation



On Thu, 6 Sep 2007, Clooney, David wrote:

> Hi All
>
>
>
> Is there any chance someone could clarify MPX for me.
>
>
>
> If you have MPX set to 4 for example and there are 4 streams hitting 
> the drive. All 4 streams are writing in parallel as the tape spins. 
> And if 3 streams are writing at 15mb/sec and 1 stream is writing at 
> 10mb/sec, would the slower of the streams be a bottle neck for the 
> other 3. My lack of the tape technology is most probably to blame, I 
> am thinking of each stream the way fragments work on a tape , finish 1 
> start the next , please tell me this is not the same on each stream.
>

That is a good question, but I don't think so(?) I think the 3 streams a
15MB/s continue to truck along and the 10MB/s stream writes at 10MB/s but
its more stretched out, example:

15MB/s stream:
# # # # # # # # # # # # # # # #

10MB/s stream:
#   #   #   #   #   #   #   #   #

Justin.

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