Thanks for pointing that out Frederico - that is indeed exactly where the terminology came from! -Phil On 09/09/2015 05:48 PM, Padua, Federico wrote:

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): http://www.cs.dartmouth.edu/~dfk/papers/ap-workload-tr.pdf

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

Best, -Federico

...

On 09 Sep 2015, at 13:44, Shane Snyder <[email protected]> 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

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