ZFS-lighttpd2-sendfile, too high IO

Bob Friesenhahn bfriesen at simple.dallas.tx.us
Mon Sep 12 19:32:35 UTC 2011

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

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