[gpfsug-discuss] Slow performance on writes when using direct io

[Peter Hruška]

Hello Renar,

Thank you for the suggestion. I tried the configuration changes. They however do not seem to have any effect - the performance seems identical. I also tried all 4 combinations. I checked the documentation on the parameter "dioSmallSeqWriteBatching" and it states that small IOs are considered under 64kb. I've also found a parameter "dioSmallSeqWriteThreshold" but my GPFS version (5.1.9.0) claims that it's an unknown attribute.


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S přáním pěkného dne / Best regards

Mgr. Peter Hruška
IT specialista

M Computers s.r.o.
Úlehlova 3100/10, 628 00 Brno-Líšeň (mapa<https://mapy.cz/s/gafufehufe>)
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On Mon, 2024-03-11 at 13:56 +0000, Grunenberg, Renar wrote:
EXTERNÍ ODESÍLATEL

Hallo Peter,
my to cents to this.
Set the diasbleDIO=yes Parameter to DEFAULT and use the

! dioSmallSeqWriteBatching 1
  disableDIO 0
And give it a try.

Regards Renar


Renar Grunenberg
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Von: gpfsug-discuss <gpfsug-discuss-bounces at gpfsug.org>Im Auftrag von Peter Hruška
Gesendet: Montag, 11. März 2024 14:22
An: gpfsug-discuss at gpfsug.org
Betreff: [gpfsug-discuss] Slow performance on writes when using direct io

Hello,

We encountered a problem with performance of writes on GPFS when the application uses direct io access. To simulate the issue it is enough to run fio with option direct=1. The performance drop is quite dramatic - 250 MiB/s vs. 2955 MiB/s. We've tried to instruct GPFS to ignore direct IO by using "disableDIO=yes". The directive didn't have any effect. Is there any possibility how to achieve that GPFS would ignore direct IO requests and use caching for everything?


--
S přáním pěkného dne / Best regards

Mgr. Peter Hruška
IT specialista
M Computers s.r.o.
Úlehlova 3100/10, 628 00 Brno-Líšeň (mapa<https://mapy.cz/s/gafufehufe>)
T:+420 515 538 136
E: peter.hruska at mcomputers.cz<mailto:peter.hruska at mcomputers.cz>

www.mcomputers.cz<http://www.mcomputers.cz/>
www.lenovoshop.cz<http://www.lenovoshop.cz/>
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