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From: Laszlo KAROLYI <szoftos@freemail.hu>
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Subject: Re: ZFS-lighttpd2-sendfile, too high IO
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But does this explain the 4-5mbyte/s reads when having a 15mbit/s network l=
oad?

Bob Friesenhahn <bfriesen@simple.dallas.tx.us> =EDrta:
>On Mon, 12 Sep 2011, K. Macy wrote:
>
>> 2011/9/12 Steven Hartland <killing@multiplay.co.uk>:
>>> sendfile doesn&#39;t work as you might expect on zfs, its not zero copy=
 due to
>>> the use of none buffer pool memory.
>>>
>>> You do get a benefit but it requires double the amount of memory to get=
 it
>>> so we&#39;ve disabled sendfile
>>> under nginx for zfs based hosts for this very reason.
>>
>> In my performance testing, sending from mmaped I/O on ZFS was
>> dramatically faster (> 2x) than sendfile.
>
>The problem is that since the zfs ARC and the backing memory used for=20
>the mapping are not the same, twice as much memory is used.  This=20
>would not be good for streaming if the machine is short on RAM.
>
>Bob
>--=20
>Bob Friesenhahn
>bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
>GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
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