[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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