[gpfsug-discuss] Same file opened by many nodes / processes

Mon Jul 23 11:13:56 BST 2018

I think the network problems need to be cleared first. Then I would
investigate further.

Buf if that is not a trivial path...
Are you able to understand from the mmfslog what happens when the tipping
point occurs?

In my view, when troubleshooting is not easy, the usual methods work/help
to find the next step:
- Narrow the window of troubleshooting (by discarding "for now" events that
did not happen within the same timeframe)
- Use "as precise" as possible, timebased events to read the reaction of
the cluster (via log or others)  and make assumptions about other observed
situations.
- If possible and when the problem is happening, run some traces, gpfs.snap
and ask for support via PMR.

Also,

What is version of GPFS?
How many quorum nodes?
How many filesystems?
Is the management network the same as the daemon network?

On Mon, 23 Jul 2018 at 20:37, Peter Childs <p.childs at qmul.ac.uk> wrote:

> On Mon, 2018-07-23 at 00:51 +1200, José Filipe Higino wrote:
>
>
> Hi there,
>
> Have you been able to create a test case (replicate the problem)? Can you
> tell us a bit more about the setup?
>
>
> Not really, It feels like a perfect storm, any one of the tasks running on
> its own would be fine, Its the shear load, our mmpmon data says the storage
> has been flat lining when it occurs.
>
> Its a reasonably standard (small) HPC cluster, with a very mixed work
> load, hence while we can usually find "bad" jobs from the point of view of
> io on this occasion we can see a few large array jobs all accessing the
> same file, the cluster runs fine until we get to a certain point and one
> more will tip the balance. We've been attempting to limit the problem by
> adding limits to the number of jobs in an array that can run at once. But
> that feels like fire fighting.
>
>
> Are you using GPFS API over any administrative commands? Any problems with
> the network (being that Ethernet or IB)?
>
>
> We're not as using the GPFS API, never got it working, which is a shame,
> I've never managed to figure out the setup, although it is on my to do list.
>
> Network wise, We've just removed a great deal of noise from arp requests
> by increasing the arp cache size on the nodes. Its a mixed 1GBit/10GBit
> network currently, we're currently looking at removing all the 1GBit nodes
> within the next few months and adding some new faster kit. The Storage is
> attached at 40GBit but it does not look to want to run much above 5Gbit I
> suspect due to Ethernet back off due to the mixed speeds.
>
> While we do have some IB we don't currently run our storage over it.
>
> Thanks in advance
>
> Peter Childs
>
>
>
>
>
> Sorry if I am un-announced here for the first time. But I would like to
> help if I can.
>
> Jose Higino,
> from NIWA
> New Zealand
>
> Cheers
>
> On Sun, 22 Jul 2018 at 23:26, Peter Childs <p.childs at qmul.ac.uk> wrote:
>
> Yes, we run mmbackup, using a snapshot.
>
> The scan usally takes an hour, but for the last week has been taking many
> hours (i saw it take 12 last Tuesday)
>
> It's speeded up again now back to its normal hour, but the high io jobs
> accessing the same file from many nodes also look to have come to an end
> for the time being.
>
> I was trying to figure out howto control the bad io using mmchqos, to
> prioritise certain nodes over others but had not worked out if that was
> possible yet.
>
> We've only previously seen this problem when we had some bad disks in our
> storage, which we replaced, I've checked and I can't see that issue
> currently.
>
> Thanks for the help.
>
>
>
> Peter Childs
> Research Storage
> ITS Research and Teaching Support
> Queen Mary, University of London
>
> ---- Yaron Daniel wrote ----
>
> Hi
>
> Do u run mmbackup on snapshot , which is read only ?
>
>
> Regards
>
> ------------------------------
>
>
>
> *Yaron Daniel*  94 Em Ha'Moshavot Rd
> *Storage Architect – IL Lab Services (Storage)*  Petach Tiqva, 49527
> *IBM Global Markets, Systems HW Sales*  Israel
>
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>
> From:        Peter Childs <p.childs at qmul.ac.uk>
> To:        "gpfsug-discuss at spectrumscale.org" <
> gpfsug-discuss at spectrumscale.org>
> Date:        07/10/2018 05:51 PM
> Subject:        [gpfsug-discuss] Same file opened by many nodes /
> processes
> Sent by:        gpfsug-discuss-bounces at spectrumscale.org
> ------------------------------
>
>
>
> We have an situation where the same file is being read by around 5000
> "jobs" this is an array job in uge with a tc set, so the file in
> question is being opened by about 100 processes/jobs at the same time.
>
> Its a ~200GB file so copying the file locally first is not an easy
> answer, and these jobs are causing issues with mmbackup scanning the
> file system, in that the scan is taking 3 hours instead of the normal
> 40-60 minutes.
>
> This is read only access to the file, I don't know the specifics about
> the job.
>
> It looks like the metanode is moving around a fair amount (given what I
> can see from mmfsadm saferdump file)
>
> I'm wondering if we there is anything we can do to improve things or
> that can be tuned within GPFS, I'm don't think we have an issue with
> token management, but would increasing maxFileToCache on our token
> manager node help say?
>
> Is there anything else I should look at, to try and attempt to allow
> GPFS to share this file better.
>
> Thanks in advance
>
> Peter Childs
>
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>
> --
>
> Peter Childs
> ITS Research Storage
> Queen Mary, University of London
>
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