[gpfsug-discuss] sequential I/O write - performance

[Alec]

This won't affect your current issue but if you're doing a lot of large
sequential IO you may want to consider setting prefetchPct to 40 to 60
percent instead of default 20%.  In our environment that has measurable
impact, but we have a lot less ram than you do in the pagepool (8g versus
64g).

Also do you have a dedicated meta pool?  If not that could be a source of
contention.  Highly recommend a small pinnable LUN or two as a dedicated
meta pool.

Alec

On Thu, Feb 8, 2024, 7:01 AM Michal Hruška <Michal.Hruska at mcomputers.cz>
wrote:

> @Aaron
>
> Yes, I can confirm that 2MB blocks are transfered over.
>
> @ Jan-Frode
>
> We tried to change multiple parameters, but if you know the best
> combination for sequential IO, please let me know.
>
>
>
> #mmlsconfig
>
> autoload no
>
> dmapiFileHandleSize 32
>
> minReleaseLevel 5.1.9.0
>
> tscCmdAllowRemoteConnections no
>
> ccrEnabled yes
>
> cipherList AUTHONLY
>
> sdrNotifyAuthEnabled yes
>
> pagepool 64G
>
> maxblocksize 16384K
>
> maxMBpS 40000
>
> maxReceiverThreads 32
>
> nsdMaxWorkerThreads 512
>
> nsdMinWorkerThreads 8
>
> nsdMultiQueue 256
>
> nsdSmallThreadRatio 0
>
> nsdThreadsPerQueue 3
>
> prefetchAggressiveness 2
>
> adminMode central
>
>
>
> /dev/fs0
>
> @Uwe
>
> Using iohist we found out that gpfs is overloading one dm-device (it took
> about 500ms to finish IOs). We replaced the „problematic“ dm-device (as we
> have enough drives to play with) for new one but the overloading issue just
> jumped to another dm-device.
> We believe that this behaviour is caused by the gpfs but we are unable to
> locate the root cause of it.
>
>
>
> Best,
> Michal
>
>
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>
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