Date: Thu, 01 Apr 2010 19:10:05 +0000 From: Paul Wootton <paul@fletchermoorland.co.uk> To: Bartosz Stec <bartosz.stec@it4pro.pl> Cc: freebsd-fs@freebsd.org, freebsd-current@freebsd.org Subject: Re: gpart failing with no such geom after gpt corruption Message-ID: <4BB4EF8D.9090809@fletchermoorland.co.uk> In-Reply-To: <4BB49E3F.7070506@it4pro.pl> References: <4BB49E3F.7070506@it4pro.pl>
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Bartosz,
One thing to remember is that GPT stores it's header and entry tables at
both the start and end of the disk for redundancy.
As far as I understand it, by making the disk physically smaller, the
GPT primary header and entry data would have become invalid as the last
partition would now be ending past the end of the disk
Partition table format
Offset Length Content
0 8 Signature ("EFI PART", 45 46 49 20 50 41 52 54)
...
24 8 Current LBA (location of this header copy)
32 8 Backup LBA (location of the other header copy)
40 8 First usable LBA for partitions (primary partition table last
LBA + 1)
48 8 Last usable LBA (secondary partition table first LBA - 1)
...
GUID partition entry format
Offset Length Content
0 16 Partition type GUID
...
32 8 First LBA (little-endian)
40 8 Last LBA (inclusive, usually odd)
...
See http://en.wikipedia.org/wiki/GUID_Partition_Table
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