FAQ

On Thu, 9 Jun 2011, Emmanuel Noobadmin wrote:

I'm trying to resolve an I/O problem on a CentOS 5.6 server. The
process basically scans through Maildirs, checking for space usage and
quota. Because there are hundred odd user folders and several 10s of
thousands of small files, this sends the I/O wait % way high. The
server hits a very high load level and stops responding to other
requests until the crawl is done.
If the server is reduced to a crawl, it's possible that you are hitting
the dirty_ratio limit due to writes and the server has entered synchronous
I/O mode. As others have mentioned, setting noatime could have a
significant effect, especially if there are many files and the server
doesn't have much memory. You can try increasing dirty_ratio to see if it
has an effect, eg:

# sysctl vm.dirty_ratio
# sysctl -w vm.dirty_ratioP

Steve

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postedJun 9, '11 at 5:24a
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