[opensuse] fdisk/table working
Hello, It's a bit OT, but I don't know where to ask. I'm the author of the partition rescue HOWTO. Usually, when one is dealing with the partition table, there is little risk. The partition table is what it says, a table. the actual file system is written when one use mkfs, not fdisk. well... sort of. I friend of mine said yesterday that in case of *logical* partition (5 and up) the file allocation table (superbloc?) of the partition is written on a sector, at the beginning of the partition so the question: How exacltly do fdisk works. say I create one primary partition of 20Go, and the rest is extended. In the extended I write two logical partitions, then I *w* write the table. what is really written? only the MBR (sort of) partition table or is the allocation table of the partitons 5 and 6 written right now, overwriting may be some data?? My friend say yes, some data is lost. I wonder why. it's the filesystem goal to write on the logical, including it's superbloc? what do you feel? thanks jdd -- http://www.dodin.net -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
On Sunday 04 May 2008 20:45:00 jdd wrote:
I friend of mine said yesterday that in case of *logical* partition (5 and up) the file allocation table (superbloc?) of the partition is written on a sector, at the beginning of the partition
File allocation table? FAT??? Anyway, yes, the bitmap for allocated blocks (in ext*) and similar book keeping is a part of the file system, and as such stored in the partition itself. The partition table is less than 500 bytes and couldn't possibly store all such information
so the question:
How exacltly do fdisk works.
say I create one primary partition of 20Go, and the rest is extended.
In the extended I write two logical partitions, then I *w* write the table.
what is really written? only the MBR (sort of) partition table or is the allocation table of the partitons 5 and 6 written right now, overwriting may be some data??
Please stop using "allocation table" when talking about partitions. This isn't FAT Yes, in a logocal partition, there is a new partition table created at the start of it. Again, the main partition table is less than 500 bytes large and can only cope with the 4 standard partitions. For logical partitions, more room is needed
My friend say yes, some data is lost.
Which data, where? So far you have only talked about creating partitions, I'm not quite sure what you're overwriting Yes, if the logical partition previously was a normal partition that contained data, then you will be overwriting part of it. Some sort of file system metadata, most likely Anders -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
On Sun, May 4, 2008 at 9:45 PM, jdd
I friend of mine said yesterday that in case of *logical* partition (5 and up) the file allocation table (superbloc?) of the partition is written on a sector, at the beginning of the partition
If what I remember from old DOS days is correct, your friend's right. The MBR has only space for 4 partitions. When you define logical disk, as your friend said, some structure is written into the first sector of this partition and these records produce the "chain" of logical partitions. Since MS SW shall see these partitions (at least as "unknown"), I guess it should still be true. -- Mark Goldstein -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
Mark Goldstein a écrit :
The MBR has only space for 4 partitions.
the table, yes When you define logical disk,
as your friend said, some structure is written into the first sector of this partition and these records produce the "chain" of logical partitions. Since MS SW shall see these partitions (at least as "unknown"), I guess it should still be true.
I see. One place, probably at the beginning of the extended partition. 16 partitions available, four bytes offset?? 64 bytes?? I should look at this more. If one use xfs as file system, no room is left (xfs begin at the partition very first sector, no rom for grub) and, for example /dev/sda4 * 10367 19457 73023457+ f W95 Etendu (LBA) /dev/sda5 10367 10628 2104483+ 82 Linux swap / Solaris abstract of my partition table, the first logical begins exactly at the first extended sector. Where are the metadata?? (logical partitions descriptions) thanks jdd -- Jean-Daniel Dodin Président du CULTe www.culte.org -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
On Sun, May 4, 2008 at 4:50 PM, jdd sur free
Mark Goldstein a écrit :
The MBR has only space for 4 partitions.
the table, yes
When you define logical disk,
as your friend said, some structure is written into the first sector of this partition and these records produce the "chain" of logical partitions. Since MS SW shall see these partitions (at least as "unknown"), I guess it should still be true.
I see. One place, probably at the beginning of the extended partition. 16 partitions available, four bytes offset?? 64 bytes??
Sorry, its a full sector each time, and more than one sector, but the sectors are spread around. For logical partitions the MBR points at EBRs (Extended Boot Records). Each EBR only describes one logical partition that immediately follows the EBR and effectively has a linked list to the next EBR. So if you create a bunch of logical partitions, you have written a EBR at the beginning of each and every one of those logical partitions. See http://en.wikipedia.org/wiki/Extended_boot_record FYI: All of that is for the standard DOS partitioning scheme. We seem to be in the middle of a very slow transition to GUID Partition Tables (GPTs). GPTs are needed to partition a drive 2TB or larger. Linux has support. MacOS now defaults to GPTs even for boot drives. Windows 64 bit Vista support GPTs for data drives. Greg -- Greg Freemyer Litigation Triage Solutions Specialist http://www.linkedin.com/in/gregfreemyer First 99 Days Litigation White Paper - http://www.norcrossgroup.com/forms/whitepapers/99%20Days%20whitepaper.pdf The Norcross Group The Intersection of Evidence & Technology http://www.norcrossgroup.com -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
Greg Freemyer a écrit :
good link, thanks jdd -- Jean-Daniel Dodin Président du CULTe www.culte.org -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org
participants (5)
-
Anders Johansson -
Greg Freemyer -
jdd -
jdd sur free -
Mark Goldstein