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Old 11-27-2008, 06:20 PM   #1
djbob
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need to SEARCH a CYLINDER for a SUPERBLOCK


Hello all,

Please see fourth post for relevant details at this point.

I am running CentOS 5.2 x64_86. All relevant partitions are ext3.

I was running out of space on my /dev/sda8 partition, so I planned on taking some space from /dev/sda7 and giving it to /dev/sda8. I first planning on resizing sda7, then rebooting, and then resizing sda8. Here is what happened:

1) I removed the journal from /dev/sda7, turning it into ext2.
2) I resized the filesystem on /dev/sda7.
3) I used fdisk to:
___a) Remove sda7. (r...7)
___b) Remove sda8. (r...7)
___c) Recreate sda7, using the same starting cylinder but an earlier ending cylinder.
___d) Recreate sda8, using the exact same starting and ending cylinders.
___e) Write the partition table to disk.
4) I then rebooted. During startup e2fsck was run, and it spit out the following error:
Quote:
bad magic number in superblock while trying to open /dev/sda8
5) I tried to e2fsck with a good amount of possible backup superblocks. No luck.

Does anybody have any ideas as to what has happened? Any suggestions on how to fix these issues?

Thanks for all your help!
djbob

Last edited by djbob; 11-28-2008 at 02:51 PM. Reason: Title changed from "'Bad magic number on superblock' after recreating partition using fdisk" to "need to SEARCH a CYLINDER for
 
Old 11-27-2008, 07:05 PM   #2
syg00
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If everything was on cylinder boundaries that should work. Probably what happened was sda7 extended into a cylinder, and sda8 started at the next sector. I see this often (you see a + in the "fdisk -l" output).
With nothing in the way, the reallocation of sda8 would start at sector zero of that cylinder.
 
Old 11-27-2008, 08:07 PM   #3
djbob
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Thanks for your help syg00

How would it be possible to fix the partition table to start at a later sector in the cylinder? What block/KB values should I try?

Current output of fdisk -l /dev/sda:
Quote:
Disk /dev/sda: 500.1 GB, 500107862016 bytes
255 heads, 63 sectors/track, 60801 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

Device Boot Start End Blocks Id System
/dev/sda1 * 1 261 2096451 83 Linux
/dev/sda2 262 1566 10482412+ 83 Linux
/dev/sda3 1567 2871 10482412+ 83 Linux
/dev/sda4 2872 60801 465322725 5 Extended
/dev/sda5 2872 3132 2096451 82 Linux swap / Solaris
/dev/sda6 3133 3263 1052226 83 Linux
/dev/sda7 3264 50324 378017451 83 Linux
/dev/sda8 59737 60801 8554612+ 83 Linux
 
Old 11-28-2008, 02:45 PM   #4
djbob
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Let me clarify what I need to do right now:

I need to search a cylinder for a superblock. Somewhere on cylinder 59737 there is a superblock, and I need to figure out at what offset I can find that superblock.

Does anybody have any ideas as to how I could do that?

Last edited by djbob; 11-28-2008 at 02:51 PM.
 
Old 11-28-2008, 05:26 PM   #5
djbob
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TestDisk solved the problem for me
 
  


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