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



> > 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?

This is Redhat 7.3 with kernel 2.4.18-26.7 on a dual Xeon 1.8 Ghz with
2GB memory

The only change we did was to enable the highmem-io patch for the 3ware
card in the kernel.spec file. The patch is written by bcrl and is
disabled by default in the RH kernel. I'll lose the I/O performance if I
don't enable it since I have > 1GB memory, the bounce-buffer copying is
going to hurt

> 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.
> 

-- 
Yusuf Goolamabbas      Reasons to switch to FireBird
yusufg outblaze com    http://mozilla.org/projects/phoenix/why/index.html





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