ZFS-lighttpd2-sendfile, too high IO

[Laszlo KAROLYI]

Hello,

it seems that turning off sendfile() in lighttpd2 completely solved my problem.

The inactive memory usage ceased, wired memory raised for ARC cache, and I see an enormous fall of IO load under the same (or even higher) network load. The disk IO load now scales to the network load.

Something must be not right with the sendfile support in ZFS.

However, my problem solved, and I'd suggest turning off sendfile in any programs in the future, unless this bug gets fixed.

Laszlo

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