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root@debian:/home/tiger# dd  if=/dev/sda  of=/dev/sdb  bs=10240k
11447+1 records in
11447+1 records out
120034123776 bytes (120 GB) copied, 4729.59 s, 25.4 MB/s
root@debian:/home/tiger# blkid
/dev/sda1: UUID="54AF-15B1" TYPE="vfat" 
/dev/sda2: UUID="28D02E2FD02E03A2" TYPE="ntfs" 
/dev/sda5: UUID="a3464de4-5676-4ae3-b37a-a1f40708d5ec" TYPE="swap" 
/dev/sda6: UUID="8b29114c-4f89-4c96-b0c0-579ce58c7345" TYPE="ext3" 
/dev/sdb1: UUID="54AF-15B1" TYPE="vfat" 
/dev/sdb2: UUID="28D02E2FD02E03A2" TYPE="ntfs" 
/dev/sdb5: UUID="a3464de4-5676-4ae3-b37a-a1f40708d5ec" TYPE="swap" 
/dev/sdb6: UUID="d38e60d8-6bfe-49f9-a381-d89b3b9bbb7f" SEC_TYPE="ext2" TYPE="ext3" 

Why doesn't /dev/sda6's uuid equal /dev/sdb6's?


Edit, answering questions from comments:

  1. sda and sdb are same size disk
  2. The output of blkid -p is:

    root@debian:/home/tiger# blkid -p /dev/sda6  
    /dev/sda6: UUID="8b29114c-4f89-4c96-b0c0-579ce58c7345" VERSION="1.0" TYPE="ext3" USAGE="filesystem"   
    
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Are they both the same sized drives? It looks like sda was 120GB. If sdb is a different size, then data may be missing or old data may still remain. Also, I am not familiar with blkid so a reboot may be needed, but not recommended because the OS will become very, very confused if you use UUID mounting. –  Aaron D. Marasco Aug 5 '12 at 11:08
    
Could you try blkid -p ? it bypasses the cache and goes low-level. Have seen confusions with its cache before. –  tripledes Aug 5 '12 at 11:50
    
hdparm -z /dev/sdb –  BatchyX Dec 4 '12 at 8:20
1  
What about the blkid -p output for /dev/sdb6? –  derobert Dec 13 '12 at 17:35
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2 Answers

You didn't give the blkid -p output for the interesting partition (/dev/sdb6), but that'd almost certainly give 8b29114c-4f89-4c96-b0c0-579ce58c7345. I suspect if you tried:

blkid -c /dev/null

you'd get the output you expect—the UUIDs would match.

You're just seeing the effects of a stale cache /etc/blkid.tab and you can fix it by:

echo -n > /etc/blkid.tab
blkid

That'll empty and regenerate the cache.

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If I read correctly your question, only ext3 partition show a different UUID. This might be something related to the file system type, so you better investigate about ext2 properties.

Could you check if tune2fs display the same UUID as blkid for /dev/sd[ab]6?

What happen when you try to set UUID on sdb6 using the same UUID of sdb6? Does tune2fs complains? Does it explain about it?

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