On 07/23/2007 03:48 PM, Theodore Tso wrote:
On Mon, Jul 23, 2007 at 09:34:25AM +0200, Rene Herman wrote:
That's not quite correct. Logicals have a start field relative to the
encompassing extended (ie, for me always 1, for others often always 63) and
the encompassing extended are relative not to the previous extended but to
the level 0 extended (the one in the MBR).
This assumes that the extended partition is at the beginning of the
disk, yes?
Err, well, no, that's not what I meant. The "start" field for the extended
partition that sits in the primary partitition table (the one in the MBR) is
absolute, or "relative to the start of the disk", but the "start" field for
the empty extended partitions that together form the logical partition list
are relative not to the previous one in the list, but all to this outermost
extended partition.
Why would anyone do that? I normally have /dev/hda1 at the beginning of
the disk, and I normally make /dev/hda4 my extended, and place it *after*
partitions at /dev/hda2, /dev/hda3, etc.
... but having said that, I do actually have an extended partition as my
/dev/hda1 at the beginning of the disk. This is the current layout on my
main system:
Device Boot Start End #sectors Id System
/dev/sda1 1 231733119 231733119 85 Linux extended
/dev/sda2 * 231733120 240121727 8388608 c W95 FAT32 (LBA)
/dev/sda3 0 - 0 0 Empty
/dev/sda4 0 - 0 0 Empty
/dev/sda5 2 2097153 2097152 82 Linux swap
/dev/sda6 2097155 18874370 16777216 83 Linux
/dev/sda7 18874372 35651587 16777216 83 Linux
/dev/sda8 35651589 231733119 196081531 83 Linux
As you can see, everything neatly non-cylinder-aligned, with not a single
sector wasted ;-) Table sectors at 0 (MBR), 1 (outer extended), 2097154,
18874371 and 35651588 (list-extendeds).
/dev/sda2 used to be a FreeBSD install (partition type 0xa5), /dev/sda3 a
MINIX install (type 0x81) and /dev/sda4 the still present FAT32 Windows 98
partition at the very end of the disk. I removed FreeBSD and MINIX due to
space shortage...
The reason that I use the first entry for an extended is that I view the
type "Linux Extended" simply as "Linux": That is, I see 0x85 simply as the
one and only Linux type with all my Linux data partitions on the logicals
inside -- very much like 0xa5 is the one FreeBSD type with all its data
partitions on the slices inside, and 0x81 the one MINIX partition with its
data partitions on the subpartitions inside.
That is, I've been using a "Linux native partitioning scheme" where the
Linux native layout just happens to coincide with a DOS/Windows native layout.
My Linux partition is at the start of the disk since it's the system I use.
The others are/were there just to boot perhaps a few times a year to check
some things -- and the start of the disk is the fastest bit, so I certainly
want my main system to use that.
Anyone find my "Native Linux Partitioning Scheme" interesting? Designing and
using a better way than regular logicals to carve up the space inside (such
as something designed after BSD slices) would work for me as well ;-)
It would be interesting to see how badly modern Windows systems breaks
on this. If Windows 2000 and above works, and Linux works, then if
other things break it might be quite sufficient to consider them
"broken software" that we don't need to worry about.
Googling for it, the 2TB limit of DOS partitioning is widely known and there
would be no point worrying even about the single-bit overflow possibly of
the list of extendeds...
With 32-bit values (and 512-byte sectors) you can service 2TB -- anything
above that requires something better than MS-DOS partition tables.
Well, in about 2-3 years or so we'll seeing having singleton disks
bigger 2TB. I'm not terribly sanguine about BIOS vendors and OS
providers migrating to something better by then, alas. Life is sure
going to be interesting. :-)
And sectors probably larger than 512 bytes. I hope they'll not do _that_
until plain old partitions are truly abandoned since before you know it
someone going to view it as an excuse to keep using this fragile mess ;-)
Rene.
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