[gpfsug-discuss] Meaning of API Stats Category

[Oesterlin, Robert]

Can you tell me how LROC plays into this? I’m trying to understand if the difference between gpfs_ns_bytes_read and gpfs_is_bytes_read on a cluster-wide basis reflects the amount of data that is recalled from pagepool+LROC (assuming the majority of the nodes have LROC.

Any insight on LROC stats would helpful as well.

[cid:image001.png at 01D2E3A4.63CEE1D0]

Bob Oesterlin
Sr Principal Storage Engineer, Nuance
507-269-0413



From: <gpfsug-discuss-bounces at spectrumscale.org> on behalf of IBM Spectrum Scale <scale at us.ibm.com>
Reply-To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date: Monday, June 12, 2017 at 4:01 PM
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Subject: [EXTERNAL] Re: [gpfsug-discuss] Meaning of API Stats Category

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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