[gpfsug-discuss] Meaning of API Stats Category

[IBM Spectrum Scale]

Hello Kristy,

The GPFSFileSystemAPI and GPFSNodeAPI sensor metrics are from the point of 
view of "applications" in the sense that they provide stats about I/O 
requests made to files in GPFS file systems from user level applications 
using POSIX interfaces like open(), close(), read(), write(), etc.

This is in contrast to similarly named sensors without the "API" suffix, 
like GPFSFilesystem and GPFSNode.  Those sensors provide stats about I/O 
requests made by the GPFS code to NSDs (disks) making up GPFS file 
systems.

The relationship between application I/O and disk I/O might or might not 
be obvious.  Consider some examples.  An application that starts 
sequentially reading a file might, at least initially, cause more disk I/O 
than expected because GPFS has decided to prefetch data.  An application 
write() might not immediately cause a the writing of disk blocks due to 
the operation of the pagepool.  Ultimately, application write()s might 
cause twice as much data written to disk due to the replication factor of 
the file system.  Application I/O concerns itself with user data; disk I/O 
might have to occur to handle the user data and associated file system 
metadata (like inodes and indirect blocks).

The difference between GPFSFileSystemAPI and GPFSNodeAPI: 
GPFSFileSystemAPI reports stats for application I/O per filesystem per 
node; GPFSNodeAPI reports application I/O stats per node.  Similarly, 
GPFSFilesystem reports stats for disk I/O per filesystem per node; 
GPFSNode reports disk I/O stats per node.

I hope this helps.
Eric Agar


Regards, The Spectrum Scale (GPFS) team

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From:   "Oesterlin, Robert" <Robert.Oesterlin at nuance.com>
To:     gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date:   06/12/2017 04:43 PM
Subject:        Re: [gpfsug-discuss] Meaning of API Stats Category
Sent by:        gpfsug-discuss-bounces at spectrumscale.org



Hi Kristy
 
What I *think* the difference is:
 
gpfs_fis: - calls to the GPFS file system interface
gpfs_fs: calls from the node that actually make it to the NSD 
server/metadata
 
The difference being what’s served out of the local node pagepool.
 
Bob Oesterlin
Sr Principal Storage Engineer, Nuance

 
From: <gpfsug-discuss-bounces at spectrumscale.org> on behalf of Kristy 
Kallback-Rose <kkr at lbl.gov>
Reply-To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date: Monday, June 12, 2017 at 3:17 PM
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Subject: [EXTERNAL] [gpfsug-discuss] Meaning of API Stats Category
 
Hi, 
 
  Can anyone provide more detail about what is meant by the following two 
categories of stats? The PDG has a limited description as far as I could 
see. I'm not sure what is meant by Application PoV. Would the Grafana 
bridge count as an "application"?
 
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