[Darshan-users] Interpretting Darshan rport

Padua, Federico padua at uni-mainz.de
Wed Sep 9 16:48:03 CDT 2015

Hi Richard,
Hi Shane,

if I may add something just to give some credits, one of the original definitions and distinctions between consecutive and sequential access appears in the early paper in 1996 titled:
File-Access Characteristics of Parallel Scientific Workloads,
also known as Charisma project.
Probably some work before that had defined it but I don’t know it, that’s the “oldest” I’m aware of...

The definition is also mentioned here (same project, same authors):

From what it appears from the Darshan plots, they use this convention as Shean well explained.


> On 09 Sep 2015, at 13:44, Shane Snyder <ssnyder at mcs.anl.gov> wrote:
> 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
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>> E:    richard-hedges at llnl.gov
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