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To: Colin Percival <colin.percival@wadham.ox.ac.uk>
From: "Poul-Henning Kamp" <phk@phk.freebsd.dk>
In-Reply-To: Your message of "Thu, 11 Mar 2004 06:41:06 GMT."
             <6.0.1.1.1.20040311063721.03e220b8@imap.sfu.ca> 
Date: Thu, 11 Mar 2004 08:17:17 +0100
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cc: cvs-src@FreeBSD.org
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Subject: Re: cvs commit: src/sys/sys mdioctl.h src/sys/dev/md md.c
	src/sbin/mdconfig mdconfig.8 mdconfig.c 
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In message <6.0.1.1.1.20040311063721.03e220b8@imap.sfu.ca>, Colin Percival writ
es:
>At 06:35 11/03/2004, Poul-Henning Kamp wrote:
>>In message <6.0.1.1.1.20040311062306.03f9ade0@imap.sfu.ca>, Colin Percival 
>>writ
>>es:
>> ><kernelnewbie>
>> >   Is it really necessary for vnode-backed memory disks to be
>> >accessed through the filesystem?  Why can't md(4) hijack the
>> >disk blocks which constitute the file (telling the filesystem
>> >not to touch them, of course) and translate I/O operations
>> >directly into I/O on the underlying device?
>> ></kernelnewbie>
>>
>>That would be a really complex solution to a problem which should not
>>exist in the first place :-)
>
>   Well... yes, but it *would* make sure that data didn't get passed
>back up to the filesystem layer.  And it would probably be faster,
>which is why I thought of it.

This is all true, but as I said, IMO the benefits does not outweigh
the added complexity.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.