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From: | Daniel Maher |
Subject: | Re: [Gluster-devel] successive bonnie++ tests taking longer and longer to run (system load steadily increasing) |
Date: | Tue, 02 Mar 2010 10:30:39 +0100 |
User-agent: | Thunderbird 2.0.0.23 (X11/20090817) |
Daniel Maher wrote:
Raghavendra G wrote: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 :Mostly reads are being served from io-cache?Perhaps ; it is worth noting that even though the operations are consistent, the data are being generated randomly. I concede that, statistically speaking, some of those 0's and 1's would be cached effectively, but this shouldn't account for a sudden ~ 50% increase in efficiency that, just as suddenly as it appears, disappears again.While it is irresponsible to extrapolate based on three points, my newest test run with io-cache disabled has yielded 10m30s, 10m36s, and 10m34s so far...
After hundreds of iterations the average « real » time per run was 10m25.522s . This was with io-cache totally disabled.
Thus, it has been shown that given a series of systematic read and write operations on progressively larger files filled with random data, the usage of io-cache is not appropriate (and will cause severe performance problems).
Of course, one could have postulated this intuitively - but there's nothing like some hard data to back up a hypothesis. :)
The real mystery is why the test with a small io-cache yielded two groups of highly varient TTCs...
-- Daniel Maher <dma+gluster AT witbe DOT net>
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