[gpfsug-discuss] QoS question

[Marc A Kaplan]

Yes, in QOS for 4.2.0 there are some simple assumptions that may not make 
a lot of sense in some configurations, especially configurations with many 
(100s) of nodes mounting the same file system...    You can try out what 
you suggested and in 4.2.0 I think it will pretty much work as you suggest 
-- essentially you are allocating 466 maintenance iops to every node, 
knowing that most of those nodes will not be using their allocation of 
IOPS.

In later releases, you may find that we will address some of these kinds 
of quirks in QOS.

QOS is a new feature for GPFS, and I don't think you'll find anything like 
it in any commercial file system offering.  (Correct me with example(s) if 
I am wrong on this point.)
So think of it as "release 1.0" (of QOS) and let us know how well it works 
for you and how it might be improved....

--marc of Spectrum(GP)FS



From:   "Buterbaugh, Kevin L" <Kevin.Buterbaugh at Vanderbilt.Edu>
To:     gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date:   06/14/2016 04:50 PM
Subject:        [gpfsug-discuss] QoS question
Sent by:        gpfsug-discuss-bounces at spectrumscale.org



Hi All, 

We have recently upgraded to GPFS 4.2.0-3 and so I am getting ready to 
dive into my first attempts at using the new QoS features.  I want to make 
sure I am understanding the documentation:

"The IOPS values that you set in an mmchqos command apply to all I/O 
operations that are issued by all the nodes that have the specified file 
system mounted. You should adjust your allocations of IOPS accordingly. 
For example, if you 600 IOPS to the maintenance class, and there are six 
nodes that have the file system mounted, then QoS allocates 100 IOPS to 
the maintenance class of each node. If you then run maintenance commands 
that affect only three of the nodes, the commands runs with an actual 
allocation of 300 IOPS, or 100 IOPS per node. To run maintenance commands 
that affect three nodes with an actual allotment of 600 IOPS, or 200 per 
node, allocate 1200 IOPS to the maintenanceclass. "
We have a ~700 node cluster with 15 NSD servers.  Here’s how I interpret 
the above assuming that I have determined that I want to allow 7,000 IOPs 
… please correct me if I’m wrong...

7,000 IOPs / 700 nodes would be 10 IOPs per node.

But I want those 7,000 IOPs to be divided amongst my 15 NSD servers that 
are going to be doing the maintenance (a restripe, for example), so 7,000 
/ 15 = 466.67.

466.67 * 700 (nodes in cluster) = 326,666.67.  So I would allocate 326,666 
IOPs to the maintenance class?

Thanks in advance…

Kevin
—
Kevin Buterbaugh - Senior System Administrator
Vanderbilt University - Advanced Computing Center for Research and 
Education
Kevin.Buterbaugh at vanderbilt.edu - (615)875-9633


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