[gpfsug-discuss] Clarification of mmdiag --iohist output

[Buterbaugh, Kevin L]

Hi All,

Been reading man pages, docs, and Googling, and haven’t found a definitive answer to this question, so I knew exactly where to turn… ;-)

I’m dealing with some slow I/O’s to certain storage arrays in our environments … like really, really slow I/O’s … here’s just one example from one of my NSD servers of a 10 second I/O:

08:49:34.943186  W        data   30:41615622144   2048 10115.192  srv   dm-92                  <client IP redacted>

So here’s my question … when mmdiag —iohist tells me that that I/O took slightly over 10 seconds, is that:

1.  The time from when the NSD server received the I/O request from the client until it shipped the data back onto the wire towards the client?
2.  The time from when the client issued the I/O request until it received the data back from the NSD server?
3.  Something else?

I’m thinking it’s #1, but want to confirm.  Which one it is has very obvious implications for our troubleshooting steps.  Thanks in advance…

Kevin
—
Kevin Buterbaugh - Senior System Administrator
Vanderbilt University - Advanced Computing Center for Research and Education
Kevin.Buterbaugh at vanderbilt.edu<mailto:Kevin.Buterbaugh at vanderbilt.edu> - (615)875-9633

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