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Date: Thu, 24 Jul 2003 08:46:13 -0700 (PDT)
From: Tom Samplonius <tom@sdf.com>
To: Scott Long <scottl@freebsd.org>
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cc: freebsd-scsi@freebsd.org
cc: Josh Brooks <user@mail.econolodgetulsa.com>
Subject: Re: aaccli: what kind of disk is it ?
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On Thu, 24 Jul 2003, Scott Long wrote:

> Tom Samplonius wrote:
> > On Wed, 23 Jul 2003, Josh Brooks wrote:
> > 
> >>I have studied the help/usage for aaccli for quite a while, and I cannot
> >>figure out how to do two things:
> >>
> >>a) how can I determine the actual, real size of the disk ?  For instance,
> >>I have some 36gig drives that are 36.8 gigs unformatted size, and some
> >>that are 36.4, and so on - if I want to buy a replacement drive to, say,
> >>rebuild a mirror, I have to get one that is the same size or larger - so
> >>how, in aaccli, can I see the actual unformatted size of that disk ?
> > 
> > 
> >   Most RAID devices do rounding:  4, 9, 18, 36, 72, etc.  So if the device
> > is a fraction bigger, it just rounds its capacity down to the standard
> > size.
> 
> Not true.

  Really?  I've never seen one that didn't.  Replacing disks is a basic
requirement of RAID, so it seems odd that anyone would want to make it
hard to do.  Do you know the which devices don't do this?

> > Besides, if you are doing RAID1 or RAID5, the controller can only
> > use as much capacity as the smallest disk in the set.  So, if you mirror
> > a 9GB and 18GB, you will only get a 9GB set.  
> > 
> 
> The point of the question was that if a failed disk is replaced with one
> that is fractionally smaller, it won't work.
> 
> Scott


Tom