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Date: Sun, 13 Jul 2003 22:01:37 -0500
From: Marc Wiz <marc@wiz.com>
To: "Greg 'groggy' Lehey" <grog@freebsd.org>
Message-ID: <20030714030137.GG50589@freshaire.wiz.com>
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cc: Dan Nelson <dnelson@allantgroup.com>
cc: Marc Wiz <marc@wiz.com>
cc: freebsd-questions@freebsd.org
Subject: Re: vinum and hot-swapping
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X-List-Received-Date: Mon, 14 Jul 2003 03:01:45 -0000

On Mon, Jul 14, 2003 at 11:49:14AM +0930, Greg 'groggy' Lehey wrote:
> On Sunday, 13 July 2003 at 20:57:46 -0500, Marc Wiz wrote:
> > On Mon, Jul 14, 2003 at 10:02:58AM +0930, Greg 'groggy' Lehey wrote:
> >>> I don't believe vinum can optimize full-stripe writes, though, since
> >>> FreeBSD can only do I/O in 64k max chunks,
> >>
> >> 128 kB.
> >
> > I thought physio was limited to 64 KB?  The man page on dump states
> > this.  Please correct me if I am wrong.
> 
> Physio is limited to MAXPHYS, which you'll find defined in
> /usr/include/sys/param.h:
> 
>   #ifndef MAXPHYS
>   #define MAXPHYS		(128 * 1024)	/* max raw I/O transfer size */
>   #endif
> 

That's nice to know.  What prevents it from being increased beyond
128K?

> I've taken a look at the dump code (yuk!), and it no longer places any
> limitation on the block size.  I'll fix the man page.
> 

Thanks.  I have tried increasing the block size but going past 64K
does not seem to help performance.  I will have to check the dump
code to see if it is limiting itself to a max of 64K.

Thanks!

Marc

-- 
Marc Wiz
marc@wiz.com
Yes, that really is my last name.