[gpfsug-discuss] Long IO waiters and IBM Storwize V5030

[Andrew Beattie]

Hi Oluwasijibomi,

If you set up a Storage Insights Standard account
You can monitor the performance of your 5030, and pull the performance
metrics of the block storage array when you see poor performance in your
scale cluster.
This will give you some idea as to what is happening,
but The 5030 is designed to be a backup / low IOPS Storage controller, the
processing power and memory in the controllers is very limited.

If you have significant workload happening on your file system in terms of
user access (reads / writes) I am not at all surprised your seeing
performance bottleneck from the 5030.

You could ask you local IBM Presales team to perform a StorM disk model of
the expected performance using your current configuration to show you what
you performance should look like.

Regards

Andrew Beattie
Technical Sales - Storage for Data and AI
IBM Australia and New Zealand

> On 29 May 2021, at 06:04, Uwe Falke <UWEFALKE at de.ibm.com> wrote:
>
> Hi, odd prefetch strategy would affect read performance, but write
latency
> is claimed to be even worse ...
> Have you simply checked what the actual IO performance of the v5k box
> under that load is and how it compares to its nominal performance and
that
> of its disks?
> how is the storage organised? how many LUNs/NSDs, what RAID code (V5k
> cannot do declustered RAID, can it?), any thin provisioning or other
> gimmicks in the game?
> what IO sizes ?
> tons of things to look at.
>
> Mit freundlichen Grüßen / Kind regards
>
> Dr. Uwe Falke
> IT Specialist
> Hybrid Cloud Infrastructure / Technology Consulting & Implementation
> Services
> +49 175 575 2877 Mobile
> Rochlitzer Str. 19, 09111 Chemnitz, Germany
> uwefalke at de.ibm.com
>
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>
> From:   Jan-Frode Myklebust <janfrode at tanso.net>
> To:     gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
> Date:   28/05/2021 19:50
> Subject:        [EXTERNAL] Re: [gpfsug-discuss] Long IO waiters and IBM
> Storwize V5030
> Sent by:        gpfsug-discuss-bounces at spectrumscale.org
>
>
>
>
> One thing to check: Storwize/SVC code will *always* guess wrong on
> prefetching for GPFS. You can see this with having a lot higher read data

> throughput on mdisk vs. on on vdisks in the webui. To fix it, disable
> cache_prefetch with "chsystem -cache_prefetch off".
>
> This being a global setting, you probably only should set it if the
system
> is only used for GPFS.
>
>
>   -jf
>
> On Fri, May 28, 2021 at 5:58 PM Saula, Oluwasijibomi <
> oluwasijibomi.saula at ndsu.edu> wrote:
> Hi Folks,
>
> So, we are experiencing some very long IO waiters in our GPFS cluster:
>
> #  mmdiag --waiters
>
> === mmdiag: waiters ===
> Waiting 17.3823 sec since 10:41:01, monitored, thread 21761 NSDThread:
for
> I/O completion
> Waiting 16.6140 sec since 10:41:02, monitored, thread 21730 NSDThread:
for
> I/O completion
> Waiting 15.3004 sec since 10:41:03, monitored, thread 21763 NSDThread:
for
> I/O completion
> Waiting 15.2013 sec since 10:41:03, monitored, thread 22175
>
> However, GPFS support is pointing to our IBM Storwize V5030 disk system
as
> the source of latency. Unfortunately, we don't have paid support for the
> system so we are polling for anyone who might be able to assist.
>
> Does anyone by chance have any experience with IBM Storwize V5030 or
> possess a problem determination guide for the V5030?
>
> We've briefly reviewed the V5030 management portal, but we still haven't
> identified a cause for the increased latencies (i.e. read ~129ms, write
> ~198ms).
>
> Granted, we have some heavy client workloads, yet we seem to experience
> this drastic drop in performance every couple of months, probably
> exacerbated by heavy IO demands.
>
> Any assistance would be much appreciated.
>
>
> Thanks,
>
> (Siji) Saula
> HPC Systems Administrator  /  Information Technology
>
> Research 2 Building 220B / Fargo ND 58108-6050
> p: 701.231.7749 / www.ndsu.edu
>
>
>
>
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