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Date:      Fri, 22 Nov 2002 00:04:58 +0000
From:      Matthew Seaman <m.seaman@infracaninophile.co.uk>
To:        FreeBSD List <questions@FreeBSD.ORG>
Subject:   Re: A question of where to put swap
Message-ID:  <20021122000458.GA79549@happy-idiot-talk.infracaninophi>
In-Reply-To: <20021121234453.GA62470@raggedclown.net>
References:  <20021121234453.GA62470@raggedclown.net>

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On Fri, Nov 22, 2002 at 12:44:54AM +0100, Cliff Sarginson wrote:
> I am in the business of re-arranging my disk layouts to reflect the
> realities if life :)
> My FreeBSD system currently runs on a SCSI-3 Disk, but I have two
> modern, fast IDE disks that will be gaining a considerable amount of
> free space in the re-arrangements. I tend to run during the course of
> the day several extremely memory loving programs which cause
> paging/swapping to occur. I would like opinions on whether I would
> notice an improvement if I moved the swap area (which lives on the SCSI
> disk with the rest of the system) to the front of one of the IDE disks.
> I intend to make a new slice on the IDE disk anyway.

A good thing to do is to put a swap partition on each disk[*].  That
permits the system to maximize IO throughput while paging.  You can
divide up your total required swap space between the three disks
however you want, but remember that to be able to get a system crash
dump, you need at least one of your swap areas to be slightly larger
than the amount of RAM in your machine.  Having approximately equally
sized swap areas gets the absolute maximum performance out of the
machine --- see The Handbook, Section 6.2.1.2
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/configtuning-initial.html

	Cheers,

	Matthew

[*] so long as the IDE drives are on different channels --- you won't
gain anything by having swap areas (or any areas of high disk IO for
that matter) on both Master and Slave on the same channel.

-- 
Dr Matthew J Seaman MA, D.Phil.                       26 The Paddocks
                                                      Savill Way
                                                      Marlow
Tel: +44 1628 476614                                  Bucks., SL7 1TH UK

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