Mailinglist Archive: opensuse (1503 mails)

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Re: [opensuse] Re: Partitioning problem in installing oS v11.1
  • From: "Boyd Stephen Smith Jr." <bss@xxxxxxxxxxxxxxxxx>
  • Date: Thu, 1 Oct 2009 10:28:35 -0500
  • Message-id: <200910011028.46293.bss@xxxxxxxxxxxxxxxxx>
On Thursday 01 October 2009 09:54:36 Greg Freemyer wrote:
On Thu, Oct 1, 2009 at 10:08 AM, Per Jessen <per@xxxxxxxxxxxx> wrote:
Stan Goodman wrote:
I think, in fact, that HDs have two copies of the partition table.

Yes, it does.

Only for GPT. Old-style "DOS" partition tables were only had one copy, at the
beginning of the drive.

Are you guys sure about that?

Yes. GPT requires two copies of the partition table. One is at the front of
the drive, one is at the end of the drive. Both have a checksum as part of
their data. If the checksum for one is invalid, it is ignored and the other
copy used instead.

Is that a unique Linux thing?

No. It is unique to GPT, AFAIK. BSD and Solaris disk labels didn't use two
copies and neither do DOS-style partition tables.

Where is
the second copy?

At the end of the drive.

The MBR (master boot record) (which includes the partition table)

When using GPT partition tables, neither copy is stored in the MBR. Instead,
a "compatibility" partition table is stored where the DOS-style partition
table would be (in the MBR). This compatibility table will contain one
(primary) partition of type EE and (optionally) partitions (also primary)
corresponding to the first 3 partitions in the GPT table.

The compatibility table is ignored by systems that expect GPT partitions. For
systems that support both the "DOS" partition tables and GPT partitions, the
partition of type EE indicates that GPT is used on this disk. The extents of
the EE partition do not matter; the GPT is always at a fixed location from the
beginning (and end) of a drive and this is not affected by the extents of the
EE partition in the compatibility partition table.
Boyd Stephen Smith Jr. ,= ,-_-. =.
bss@xxxxxxxxxxxxxxxxx ((_/)o o(\_))
ICQ: 514984 YM/AIM: DaTwinkDaddy `-'(. .)`-' \_/

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