[gpfsug-discuss] AFM: Slow startup of flush from cache to home

[Billich Heinrich Rainer (PSI)]

Hello,

Running an AFM IW cache  we noticed that AFM starts the flushing of data from cache to home rather slow, say at 20MB/s, and only slowly increases to several 100MB/s after a few minutes. As soon as the pending queue gets no longer filled the data rate drops, again.

I assume that this is a good behavior for WAN traffic where you don’t want to use the full bandwidth from the beginning but only if really needed. For our local setup with dedicated links I would prefer a much more aggressive behavior to get data transferred asap to home.

Am I right, does AFM implement such a ‘slow startup’, and is there a way to change this behavior? We did increase afmNumFlushThreads  to 128. Currently we measure with many small files (1MB). For large files the behavior is different, we get a stable data rate from the beginning, but I did not yet try with a continuous write on the cache to see whether I see an increase after a while, too.

Thank you,

Heiner Billich

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Paul Scherrer Institut
Science IT
Heiner Billich
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CH 5232  Villigen PSI
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