On 2009/12/09 20:06 (GMT+0100) jdd-gmane composed:
Felix Miata wrote:
The reason for distinguishing between "primary" and "logical" partitions applies entirely to the boot process
that's not true.
Yes it is.
In fact I had the same thinking for several years. But as the author of the Partition Rescue HOWTO, I was made aware by a reader that logical partitions have to store the Inodes/fat somewhere and this somewhere is the first sector of the partition.
It looks like there's some kind of communication failure going on here, or else that "reader" didn't actually know what he was talking about.
So very soon after the logical partition creation some bits are written to the drive on theses sectors. If you happen to have data there, you can lose things.
There is no overlap between legacy BIOS compatible partitioning information and filesystem space. The two share exactly 0 sectors. Filesystems write their FAT and Inode data in filesystem space, not boot record/partition table space. In fact regarding the partition tables and the partitions themselves, the layout of a primary beginning at the start of a disk is nearly identical to every logical partition, and quite different from primary partitions occupying partition table entries 2-4, which is why an extended partition cannot begin at the very start of a disk. Here is an example taken from this legacy BIOS compatible system, on which the extended occupies the last MBR partition table entry: Part Cyl Head Sect sda1 0 1 1 sda2 26 0 1 sda3 332 0 1 sda5 363 1 1 The above table lists the start of the _filesystems_ whose logical locations on the disk are as defined in the MBR and first EBR sector. Note that the first primary and all logicals begin on the second physical head, rather than as primaries 2-4 that begin on the first physical head. There are circumstances when data is written outside filesystem space that has no direct bearing on either the tables or the filesystems, such as LVM data, IBM Boot Manager data, OnTrack overlays, malware, or software RAID data. None of these are relevant post-boot to whether a partition is "logical" or "primary".
This is important when one have lost the partition table and don't
If you've lost the partition tables you just need a competent tool designed to recover them. If you happen to have saved partitioning information on paper that just makes recovery easier.
have the exact data on paper. Using guesses can destroy some bits of data.
Whatever information a filesystem stores about its disk location within its own space is entirely up to its designer. If its OS user determines in some way what to put there based upon the location of the sector containing the partition table entry defining it isn't within the scope of this discussion. There's no need for such data to be there, as all the OS needs to know about the partition's definition is what it finds in the partition tables. Whatever it chooses to put in its own space is a matter of its own convenience or design.
there is no similar problem for primaries, as they data is in the first disk sector, never used for storing data
The architecture of a partition's first sector is not necessarily different according to whether it's on head zero (non-first primary) or head one (first primary or logical). Whatever needs to be there needs to be there regardless, and usually is a volume boot record. -- " We have no government armed with power capable of contending with human passions unbridled by morality and religion." John Adams, 2nd US President Team OS/2 ** Reg. Linux User #211409 Felix Miata *** http://fm.no-ip.com/ -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org