[lustre-discuss] Meaning of 'slow creates' messages on MDS

Russell Dekema dekemar at umich.edu
Tue May 30 12:37:54 PDT 2017

On Tue, May 30, 2017 at 12:20 PM, Oleg Drokin <oleg.drokin at intel.com> wrote:
> This means exactly what it says.
> This ost is slow creating new objects (for the object preallocates).
> If all of your OST creates are slow - then when you create a lot of files,
> eventually you run out of OST objects (or when striping is used,
> just on a few of them) and MDT threads doing creates start to block.
> If all MDT threads block then no more new requests could be processed and you'd
> see general fs slowness. Otherwise the slowness would just be localized to the directories where the files are being created.
> Overall it looks like your OSTs are overloaded. You might want to try faster storage or
> decrease number of ost io threads to ease the (parallel) load.
> Hope this helps.
> Bye,
>     Oleg

Thank you very much for the detailed explanation - I think that will
help us quite a bit.

Prior to your reply, I wasn't sure whether the message meant the OST
was slow at creating new objects thus making the MDT wait, or whether
the MDT was being slow thus making the OST wait, and you have cleared
that up for us very nicely.

Rusty Dekema
University of Michigan
Advanced Research Computing - Technical Services

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