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Re: [Gluster-devel] successive bonnie++ tests taking longer and longer

From: Daniel Maher
Subject: Re: [Gluster-devel] successive bonnie++ tests taking longer and longer to run (system load steadily increasing)
Date: Thu, 25 Feb 2010 10:38:41 +0100
User-agent: Thunderbird (X11/20090817)

Raghavendra G wrote:
Hi Daniel,

Can you decrease the cache size in io-cache (say to 128MB)? If the files being served are bigger than this size, you can as well remove io-cache from configuration. Do let us know if this solves your issue.

Some of the files that are generated during the test are under 128M, and some are much larger - effectively, the test deals with larger and larger sets of data as it runs its course.

At your suggestion, i changed the io-cache size from the default setting (as generated by the configurator) to 128M, and re-ran the test. The results are now much more consistent with what would be expected :

real    21m31.019s
real    21m30.932s
real    21m28.965s
real    21m26.095s
real    21m26.388s
real    21m29.377s
real    21m32.180s
real    21m26.600s
real    21m28.354s
(cut for brevity)

However, at two points during the multi-day test run, something strange happened. The time to completion dropped _dramatically_, and stayed there for numerous iterations, before jumping back up again :

real    21m27.806s
real    21m45.434s
real    14m41.468s
real    12m41.172s
real    12m39.779s
real    12m34.595s
real    12m42.223s
real    12m41.111s
(repeat 30 iterations)
real    12m40.185s
real    12m40.517s
real    13m25.394s
real    21m26.375s
real    21m28.476s

I am forced to assume that something else on either the client or the server nodes caused this behaviour, but i cannot imagine what. The nodes, frankly, aren't doing anything else. Very strange.

I am going to remove the io-cache entirely and see what, if any, effect that has.

Daniel Maher <dma+gluster AT witbe DOT net>

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