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Old 01-16-2004, 09:05 AM   #1
EyesOnly
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partitiontable erased. Linux can still read disk?


Hello

I got a dualboot setup whit windows 2000 and slackware 9
yesterday windows 2000 suddenly failed to boot. It appeared the partitiontable was erased.(how? dunno )
I put the disk in another windows 2000 computer, and indeed the disk showed up as empty in the disk manager.
Norton Disk Doctor could restore the partitiontable, but it was defenilty not the right one(i suddenly had 6 partitions instead of 3...)

After poking around whit many other disk doctors, warriors and whatever I was about to give up.

As a last resort, i put the disk back in my computer, and booted slackware, to see if I could get something done there.
To my biggest suprise slackware just mounted the disk as it always did, and i could access all my files, like nothing ever happend.

running fdisk from slackware to show the partitiontable also shows a serious damaged partitiontable.

So now I wonder, How could this be? How can linux read this disk without having a valid partitiontable?

(PS. I have saved all my data from this disk, and Windows 2000 is reinstalling right now. so no real problems anymore )
 
Old 01-16-2004, 11:50 AM   #2
leonscape
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Because its more forgiving? and its meant to be robust. It uses inodes, and its filesystems on the disk are quite sturdy.

Also the bootloader, knows where its files are usually by position on the disk and not through the partition table. The Linux partitions probably where still intacked and could work out how big they are.

basically very clever code, Linux has been developed to be robust.

Last edited by leonscape; 01-16-2004 at 11:52 AM.
 
Old 01-16-2004, 12:34 PM   #3
EyesOnly
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I think I forgot some things in my question.

The partition I'm talking about is a NTFS partition. The partitiontable is erased, and windows can't read it anymore(which makes sense i think..)

BUT linux can still read this partition, as if it doesn't even need this partitiontable

How could this be? if linux doesn't retrieve partition information from the partitiontable, then how does it do it?

Just curious here
 
Old 01-16-2004, 12:54 PM   #4
leonscape
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Okay you've got me here, I've no idea. I guess the guys the wrote the NTFS driver deserve applause for that one.

This is what a lot of NTFS access on Linux is for, as usually you can't write to it. So recusing a trashed disk would make sense. I think its looking at the actual files, and the way the disk is set up, to identify partitions. Which can be done.
 
Old 01-16-2004, 01:52 PM   #5
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The partition table is gone, yes. However the filesystem still exists. No, these are not the same things, and people often intermix the 2.

The reason windows cannot boot is because it has no idea where the filesystem is. Not that it doesn't exists, but that it's lost.
 
Old 01-16-2004, 02:07 PM   #6
EyesOnly
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Quote:
The reason windows cannot boot is because it has no idea where the filesystem is. Not that it doesn't exists, but that it's lost.
exactly.
But windows doesn't boot AND cannot find the files.
But linux still can find the files, which suprised me. If windows doesnt know where the filesystem is, then how can linux now where it is?
I think what leonscape said would be the only way then. But then, that would take a lot of time, right? And it didn't take a lot of time here..

Anyway, this is again another proof that linux is the best

Quote:
I guess the guys the wrote the NTFS driver deserve applause for that one.
They definetly do
 
Old 01-16-2004, 02:13 PM   #7
leonscape
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What cexshun also does make sense. The partition table only tells you where the partitions are, and how big they are. They also hold a key for which filesystem is on the partition.

Each partition holds its filesystem, which will also have details of how big it is, and theirs space between them. So all Linux would have to do is Search for the beginning of each partition. This wouldn't take long, then it can grab the info about each partition from that.

Its still pretty clever though.
 
Old 01-17-2004, 05:16 AM   #8
EyesOnly
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I did some more searching around, and found out about gpart
http://www.stud.uni-hannover.de/user/76201/gpart/

It can guess the partitions on a disk when the partitiontable is gone. That is possibly what happend in my case..

very clever indeed.
 
Old 01-17-2004, 05:30 AM   #9
cdlen
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I tell this from the back of my head but as i can record right now (early morning !) the partition table store partitions infos in a redundant manner (start and size) . With all the starts you shouldn't need the sizes and vice-versa.
Win and Linux read the data their own way. So it is possible for one to see a screwed table and for another to see it faultless..
I think this is why MS fdisk is so happy destroying others OSes' partitions.
 
  


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