[Darshan-users] Interpretting Darshan rport

[Shane Snyder]

Hi Richard,

Sequential describes I/O accesses that are just at any offset greater 
than the immediately preceding I/O operation. For instance, say I write 
100 bytes at offset 0, then my next access is a read at offset 500 -- 
that would be a sequential access.

Consecutive is more strict in that it requires that the current 
operation be at the offset immediately following the end of the 
preceding access's end. An example would be if I write 100 bytes at 
offset 0, then read at offset 100, instead. So, all consecutive accesses 
are also sequential but not vice versa.

Note that there is no distinction between the types of the 2 operations. 
If the current operation is a write, we don't care if the previous 
operation was a read or a write, just the ending offset of it.

I should probably mention that we have fixed this graph to be more clear 
in the new development branch of darshan we are preparing to release, as 
it has been a source of confusion for a number of people.

--Shane

On 09/09/2015 03:23 PM, Hedges, Richard M. wrote:
> In the default report, the fourth plot (labelled ?I/O Pattern”) 
> distinguishes between ”Consecutive” and “Sequential” .  Could someone 
> explain the distinction for me?
>
> Thanks,
> - Richard
>
> ====================================================
>
> Richard Hedges
> Customer Support and Test - File Systems Project
> Development Environment Group - Livermore Computing
> Lawrence Livermore National Laboratory
> 7000 East Avenue, MS L-557
> Livermore, CA    94551
>
> v:    (925) 423-2699
> f:    (925) 423-6961
> E:    richard-hedges at llnl.gov
>
>
>
>
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