[gpfsug-discuss] Well, this is the pits...
Kumaran Rajaram
kums at us.ibm.com
Thu May 4 18:20:41 BST 2017
>>Thanks for the info on the releases … can you clarify about
pitWorkerThreadsPerNode?
pitWorkerThreadsPerNode -- Specifies how many threads do restripe, data
movement, etc
>>As I said in my original post, on all 8 NSD servers and the filesystem
manager it is set to zero. No matter how many times I add zero to zero I
don’t get a value > 31! ;-) So I take it that zero has some sort of
unspecified significance? Thanks…
Value of 0 just indicates pitWorkerThreadsPerNode takes internal_value
based on GPFS setup and file-system configuration (which can be 16 or
lower) based on the following formula.
Default is pitWorkerThreadsPerNode = MIN(16, (numberOfDisks_in_filesystem
* 4) / numberOfParticipatingNodes_in_mmrestripefs + 1)
For example, if you have 64 x NSDs in your file-system and you are using 8
NSD servers in "mmrestripefs -N", then
pitWorkerThreadsPerNode = MIN (16, (256/8)+1) resulting in
pitWorkerThreadsPerNode to take value of 16 ( default 0 will result in 16
threads doing restripe per mmrestripefs participating Node).
If you want 8 NSD servers (running 4.2.2.3) to participate in mmrestripefs
operation then set "mmchconfig pitWorkerThreadsPerNode=3 -N
<8_NSD_Servers>" such that (8 x 3) is less than 31.
Regards,
-Kums
From: "Buterbaugh, Kevin L" <Kevin.Buterbaugh at Vanderbilt.Edu>
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date: 05/04/2017 12:57 PM
Subject: Re: [gpfsug-discuss] Well, this is the pits...
Sent by: gpfsug-discuss-bounces at spectrumscale.org
Hi Kums,
Thanks for the info on the releases … can you clarify about
pitWorkerThreadsPerNode? As I said in my original post, on all 8 NSD
servers and the filesystem manager it is set to zero. No matter how many
times I add zero to zero I don’t get a value > 31! ;-) So I take it that
zero has some sort of unspecified significance? Thanks…
Kevin
On May 4, 2017, at 11:49 AM, Kumaran Rajaram <kums at us.ibm.com> wrote:
Hi,
>>I’m running 4.2.2.3 on my GPFS servers (some clients are on 4.2.1.1 or
4.2.0.3 and are gradually being upgraded). What version of GPFS fixes
this? With what I’m doing I need the ability to run mmrestripefs.
GPFS version 4.2.3.0 (and above) fixes this issue and supports "sum of
pitWorkerThreadsPerNode of the participating nodes (-N parameter to
mmrestripefs)" to exceed 31.
If you are using 4.2.2.3, then depending on "number of nodes participating
in the mmrestripefs" then the GPFS config parameter
"pitWorkerThreadsPerNode" need to be adjusted such that "sum of
pitWorkerThreadsPerNode of the participating nodes <= 31".
For example, if "number of nodes participating in the mmrestripefs" is 6
then adjust "mmchconfig pitWorkerThreadsPerNode=5 -N
<participating_nodes>". GPFS would need to be restarted for this parameter
to take effect on the participating_nodes (verify with mmfsadm dump
config | grep pitWorkerThreadsPerNode)
Regards,
-Kums
From: "Buterbaugh, Kevin L" <Kevin.Buterbaugh at Vanderbilt.Edu>
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date: 05/04/2017 12:08 PM
Subject: Re: [gpfsug-discuss] Well, this is the pits...
Sent by: gpfsug-discuss-bounces at spectrumscale.org
Hi Olaf,
I didn’t touch pitWorkerThreadsPerNode … it was already zero.
I’m running 4.2.2.3 on my GPFS servers (some clients are on 4.2.1.1 or
4.2.0.3 and are gradually being upgraded). What version of GPFS fixes
this? With what I’m doing I need the ability to run mmrestripefs.
It seems to me that mmrestripefs could check whether QOS is enabled …
granted, it would have no way of knowing whether the values used actually
are reasonable or not … but if QOS is enabled then “trust” it to not
overrun the system.
PMR time? Thanks..
Kevin
On May 4, 2017, at 10:54 AM, Olaf Weiser <olaf.weiser at de.ibm.com> wrote:
HI Kevin,
the number of NSDs is more or less nonsense .. it is just the number of
nodes x PITWorker should not exceed to much the #mutex/FS block
did you adjust/tune the PitWorker ? ...
so far as I know.. that the code checks the number of NSDs is already
considered as a defect and will be fixed / is already fixed ( I stepped
into it here as well)
ps. QOS is the better approach to address this, but unfortunately.. not
everyone is using it by default... that's why I suspect , the development
decide to put in a check/limit here .. which in your case(with QOS)
would'nt needed
From: "Buterbaugh, Kevin L" <Kevin.Buterbaugh at Vanderbilt.Edu>
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date: 05/04/2017 05:44 PM
Subject: Re: [gpfsug-discuss] Well, this is the pits...
Sent by: gpfsug-discuss-bounces at spectrumscale.org
Hi Olaf,
Your explanation mostly makes sense, but...
Failed with 4 nodes … failed with 2 nodes … not gonna try with 1 node. And
this filesystem only has 32 disks, which I would imagine is not an
especially large number compared to what some people reading this e-mail
have in their filesystems.
I thought that QOS (which I’m using) was what would keep an mmrestripefs
from overrunning the system … QOS has worked extremely well for us - it’s
one of my favorite additions to GPFS.
Kevin
On May 4, 2017, at 10:34 AM, Olaf Weiser <olaf.weiser at de.ibm.com> wrote:
no.. it is just in the code, because we have to avoid to run out of mutexs
/ block
reduce the number of nodes -N down to 4 (2nodes is even more safer) ...
is the easiest way to solve it for now....
I've been told the real root cause will be fixed in one of the next ptfs
.. within this year ..
this warning messages itself should appear every time.. but unfortunately
someone coded, that it depends on the number of disks (NSDs).. that's why
I suspect you did'nt see it before
but the fact , that we have to make sure, not to overrun the system by
mmrestripe remains.. to please lower the -N number of nodes to 4 or
better 2
(even though we know.. than the mmrestripe will take longer)
From: "Buterbaugh, Kevin L" <Kevin.Buterbaugh at Vanderbilt.Edu>
To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
Date: 05/04/2017 05:26 PM
Subject: [gpfsug-discuss] Well, this is the pits...
Sent by: gpfsug-discuss-bounces at spectrumscale.org
Hi All,
Another one of those, “I can open a PMR if I need to” type questions…
We are in the process of combining two large GPFS filesystems into one new
filesystem (for various reasons I won’t get into here). Therefore, I’m
doing a lot of mmrestripe’s, mmdeldisk’s, and mmadddisk’s.
Yesterday I did an “mmrestripefs <old fs> -r -N <my 8 NSD servers>” (after
suspending a disk, of course). Worked like it should.
Today I did a “mmrestripefs <new fs> -b -P capacity -N <those same 8 NSD
servers>” and got:
mmrestripefs: The total number of PIT worker threads of all participating
nodes has been exceeded to safely restripe the file system. The total
number of PIT worker threads, which is the sum of pitWorkerThreadsPerNode
of the participating nodes, cannot exceed 31. Reissue the command with a
smaller set of participating nodes (-N option) and/or lower the
pitWorkerThreadsPerNode configure setting. By default the file system
manager node is counted as a participating node.
mmrestripefs: Command failed. Examine previous error messages to determine
cause.
So there must be some difference in how the “-r” and “-b” options
calculate the number of PIT worker threads. I did an “mmfsadm dump all |
grep pitWorkerThreadsPerNode” on all 8 NSD servers and the filesystem
manager node … they all say the same thing:
pitWorkerThreadsPerNode 0
Hmmm, so 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 + 0 > 31?!? I’m confused...
—
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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