[gpfsug-discuss] High I/O wait times

[Buterbaugh, Kevin L]

Hi all,

We are experiencing some high I/O wait times (5 - 20 seconds!) on some of our NSDs as reported by “mmdiag —iohist" and are struggling to understand why.  One of the confusing things is that, while certain NSDs tend to show the problem more than others, the problem is not consistent … i.e. the problem tends to move around from NSD to NSD (and storage array to storage array) whenever we check … which is sometimes just a few minutes apart.

In the past when I have seen “mmdiag —iohist” report high wait times like this it has *always* been hardware related.  In our environment, the most common cause has been a battery backup unit on a storage array controller going bad and the storage array switching to write straight to disk.  But that’s *not* happening this time.

Is there anything within GPFS / outside of a hardware issue that I should be looking for??  Thanks!

—
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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