Subject: Re: [PATCH] scsi/sd: Fix capacity output to show MB/GB/TB/...
From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Matthew Wilcox <matthew@wil.cx>
Cc: Simon Arlott <simon@fire.lp0.eu>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       linux-scsi <linux-scsi@vger.kernel.org>
In-Reply-To: <20080831025412.GJ1239@parisc-linux.org>
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Date: Sun, 31 Aug 2008 10:08:29 -0500
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On Sat, 2008-08-30 at 20:54 -0600, Matthew Wilcox wrote:
> On Sat, Aug 30, 2008 at 08:59:07PM -0500, James Bottomley wrote:
> > However, I'm afraid it needs to be a bit more sophisticated:  for
> > instance, under these calculations, a 1.75TB disk will show up as 1TB.
> > Thus, I think we need to print the capacity to 3 significant figures to
> > cope with this case.
> 
> Do you have an objection to my original suggestion of 1750GB in that
> case?  It saves faffing around with fractions and it's unlikely to
> confuse the user.
> 
> BTW, I do appreciate Simon's point about df showing a different number.
> How about we print:
> 
> sd 7:0:0:0: [sdc] 1099511627776 512-byte hardware sectors (563TB / 512TiB)
> 
> (or perhaps a more realistic number ...)
> 
> sd 7:0:0:0: [sdc] 976562500000 512-byte hardware sectors (500TB / 455TiB)
> 
> It's perhaps a more gentle way of informing our users that they may not
> have quite as much capacity as they thought they had.

OK, uncle.  We're wasting far more time on this email thread than it
would take to code the damn thing.  So, here it is as a generic helper:
both forms of calculation correctly to 3sf.

James


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