[gpfsug-discuss] Meaning of API Stats Category
IBM Spectrum Scale
scale at us.ibm.com
Wed Jun 14 01:50:24 BST 2017
Hello Bob,
Right. Within some observation interval, bytes read by an application
will be reflected in gpfs_is_bytes_read, regardless of how the byte values
were obtained (by reading from "disk", fetching from pagepool, or fetching
from LROC). gpfs_ns_bytes_read is only going to reflect bytes read from
"disk" within that observation interval.
"mmdiag --lroc" provides some LROC stats. There is also a GPFSLROC
sensor; it does not appear to be documented at this point, so I hope I
haven't spoken out of turn.
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>
Cc: "scale at us.ibm.com" <scale at us.ibm.com>
Date: 06/12/2017 06:50 PM
Subject: Re: Meaning of API Stats Category
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.
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
------------------------------------------------------------------------------------------------------------------
If you feel that your question can benefit other users of Spectrum Scale
(GPFS), then please post it to the public IBM developerWroks Forum at
https://www.ibm.com/developerworks/community/forums/html/forum?id=11111111-0000-0000-0000-000000000479
.
If your query concerns a potential software error in Spectrum Scale (GPFS)
and you have an IBM software maintenance contract please contact
1-800-237-5511 in the United States or your local IBM Service Center in
other countries.
The forum is informally monitored as time permits and should not be used
for priority messages to the Spectrum Scale (GPFS) team.
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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