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Date: Mon, 12 Sep 2011 14:32:34 -0500 (CDT)
From: Bob Friesenhahn <bfriesen@simple.dallas.tx.us>
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To: Laszlo KAROLYI <szoftos@freemail.hu>
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Cc: freebsd-fs@freebsd.org
Subject: Re: ZFS-lighttpd2-sendfile, too high IO
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On Mon, 12 Sep 2011, Laszlo KAROLYI wrote:

> But does this explain the 4-5mbyte/s reads when having a 15mbit/s network load?

There are only two viable explanations:

   o Insuffient caching due to insufficient resources

   o Data is not being cached at all

Zfs reads whole 128K blocks (or whatever the filesystem blocksize is) 
at a time.  It does not read partial blocks from underlying storage. 
This makes it very expensive to perform many small read accesses if 
the reads are not subsequently cached in the ARC.

Bob
-- 
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/