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Subject: Re: on BIOS problems with disks larger than 2 TB
To: John Baldwin <jhb@FreeBSD.org>, freebsd-hackers@FreeBSD.org
References: <6cec427b-4df1-50f0-3014-a96e5f8210f5@FreeBSD.org>
 <490347865.SvN7iQoFWI@ralph.baldwin.cx>
From: Andriy Gapon <avg@FreeBSD.org>
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Date: Fri, 12 Aug 2016 23:58:12 +0300
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On 12/08/2016 22:18, John Baldwin wrote:
> Hmm, I'm not sure how easy it is to handle this case (i.e. how do you know
> if an LBA beyond the size is really legit due to truncation vs coming from
> corrupted metadata).  Related is that tsoome's bcache stuff wants to know
> where the end of the disk is (to avoid reading off the end), so just
> ignoring the size is not easy.

One idea that I have in mind but haven't really explored yet is for GPT
formatted disks.  Basically, if a GPT label hints that the disk size is larger
than what BIOS reports, then we could try to read a backup label and if it
matches what we expect, then we could adjust the size.

Hmm, I think I recall that a long time ago some BIOSes used to do something
similar with MBR :-)

-- 
Andriy Gapon