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Re: Performance problem with mysql on a 3ware 1+0 raid array



Neil Brown wrote:

On Friday May 2, yusufg outblaze com wrote:

Neil, Thanks for the info but I am kinda confused as to why the sudden
writeout occurs at 4 minutes if the default ext3 settings is to flush
the journal every 5 seconds. Do you know what the correlation between
these times would be.



I'm not sure. There is a bug in some kernels where the time stamp of some blocks is wrong, so old data doesn't get flushed out by bdflush when it should. This can mean that data older than the bdflush interval stays in memory until it is forced out by the journal being full.

Maybe your average data rate fills the journal in about 4 minutes, and
the other bug is interfering with the regular bdflush writeout of data
blocks.

What kernel are you running?  Are you using any ext3 patches on top of
it?

RH 2.4.18-26.7 with 3ware patch enabled. No other patches besides what's in the RH distro.



NeilBrown

I have seen previous posts from you in which you described your
fileservers also having write stalls at around 5 minute intervals. Did
you figure out why things would go bad at 5 minutes interval. There
seems to be no default writeout every 5 minutes


I don't clearly remember, but I don't think I found anything that clearly pointed to 5 minutes being significant.



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