Re: 3TB disk hassles

From: Andries Brouwer
Date: Sat Dec 18 2004 - 07:16:50 EST

On Sat, Dec 18, 2004 at 03:08:42AM +0000, H. Peter Anvin wrote:
> Followup to: <20041218001254.GA8886@xxxxxxxxxxxxxxxxxxx>
> By author: Andries Brouwer <aebr@xxxxxxxxxx>
> In newsgroup:
> >
> > Yes, indeed.
> >
> > One can use a standard DOS-type partition table, and pick a new type -
> > I reserved 88 for this purpose today - where type 88 indicates a
> > plaintext partition table found elsewhere on the disk.
> > Where is elsewhere? In the starting sector of the type 88 partition
> > (that can have length 1).
> > This allows one to have the initial part of the disk (at most 2 TB)
> > partitioned in old-fashioned manner.
> >
> > The plaintext partition table is just a table with lines
> > <start> <size>
> > that one can edit with emacs or vi.
> >
> > There is magic to recognize it, namely the line
> > "# Plaintext partition table"
> > and magic to indicate the end of the table, namely "# end".
> >
> > That is all. If anybody wants it I can send the trivial code.
> > (Am using it now, but unfortunately I do not have 3 TB disks.)
> First, what's wrong with the GUID partition table format? Let's stick
> to standards as long as they work; especially for things that
> potentially affect multiple operating systems.
> Second, several problems with this. Sector 0 is the boot sector, so
> using it is a really bad choice. (I'd reserve several sector for
> master boot code.) In fact, rather than having a separate partition,
> why don't we just specify that a sector starting with "# Plaintext partition
> table" has to start within the first 64 sectors of the disk (it's
> common for DOS partition tables to have the first partition start at
> offset 63.)
> Third, it ought to be possible to put more information than this,
> e.g. for raid detect.

Concerning third, I allow for labels and comments (after #), so anybody
can add any type of recognizable comments or pragmas. The header line
and closing line are examples of comments that already have significance.

Concerning second, I think you misunderstood something. Don't know why
you think I am using MBR - certainly not to put this plaintext table.
In fact MBR has a traditional DOS-type partition table that allows for
a boot setup in traditional ways in case utilities are used that only
understand the old ways. But type 88 describes a (very short) partition
that contains the plaintext partition table. Life is easy:
# emacs partition_table
# cat partition_table > /dev/sda2
and reboot or
# blockdev --rereadpt /dev/sda

Concerning one, it is a somewhat complicated format that takes over
your disk, rather inconvenient. It seems to me that one needs a good
reason (like a BIOS that understands the format and is able to boot
from it) to choose it.

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