Date: Fri, 27 Apr 2001 08:43:28 +0930 From: Greg Lehey <grog@lemis.com> To: Scott Culverhouse <scott.culverhouse@opencube.co.uk> Cc: questions@FreeBSD.ORG Subject: Re: vinum - mirroring! Message-ID: <20010427084328.C70059@wantadilla.lemis.com> In-Reply-To: <20010426111634.C3FC.SCOTT.CULVERHOUSE@opencube.co.uk>; from scott.culverhouse@opencube.co.uk on Thu, Apr 26, 2001 at 11:19:27AM %2B0100 References: <20010426111634.C3FC.SCOTT.CULVERHOUSE@opencube.co.uk>
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On Thursday, 26 April 2001 at 11:19:27 +0100, Scott Culverhouse wrote:
> Hi we have a machine with 2 x 36Gb SCSI drives and we want to put var
> and usr on to 2 vinum volumes. But we want both performance and
> resilience can they be done with two drives only?
>
> Here is a config I propose but not sure whether it will work too well or
> not:- Is it ok?
>
> drive sd0 device /dev/da0e
> drive sd1 device /dev/da0f
You shouldn't put more than one drive on a spindle.
> drive sd2 device /dev/da1e
> drive sd3 device /dev/da1h
>
> volume var
> plex org striped 256k
You don't want a stripe size which is a power of 2.
> sd length 5g drive sd0
> sd length 5g drive sd1
> plex org striped 256k
> sd length 5g drive sd2
> sd length 5g drive sd3
>
> volume usr
> plex org striped 256k
> sd length 10g drive sd0
> sd length 10g drive sd1
This would give you terrible performance like this. You'd be adding
gratuitous seeks. The two subdisks should be on different spindles.
> plex org striped 256k
> sd length 10g drive sd2
> sd length 10g drive sd3
>
> The reason I created 4 drives (2 slices on each drive) is so I could
> have 2 drives per plex is the a good or bad idea!
It's a bad idea. That's what we have subdisks. Try this:
drive a device /dev/da0e
drive b device /dev/da1e
volume var
plex org striped 273k
sd length 5g drive a
sd length 5g drive b
plex org striped 273k
sd length 5g drive b
sd length 5g drive a
volume usr
plex org striped 273k
sd length 10g drive a
sd length 10g drive b
plex org striped 273k
sd length 10g drive b
sd length 10g drive a
Note that the subdisks on the second plex are the other way round;
otherwise the failure of a drive would cause you to lose half the
volume, which is obviously not what you want.
> What size var and usr will this give me 5g and 10g respectively!
This will give you 10g and 20g respectively.
Greg
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