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So I made a dump of one of my drives today which totalled 171GB and did a level 0 dump which had a output size of 58GB.

I dont know why it was so small, but I wanted to ask if dump searches for a past level 0 even when you instruct it to do a level 0. There is another level 0 on the drive from September.

Linux 2.6 Kernel EXt3

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Details of OS etc please. –  Jimmy Shelter Nov 24 '09 at 1:34
    
What type of "dump"? What OS? What FS? –  Insyte Nov 24 '09 at 1:34
    
Linux ext3 and dump as in Dump(8) –  Recursion Nov 24 '09 at 1:47
    
If I could enter a sufficiently short comment it would only say "Huh?" You've given the kernel version, but you haven't said what distribution. My system has no [Dd]ump or man page for it in section 8 or elsewhere. Educate us, please. –  Dennis Williamson Nov 24 '09 at 2:39
    
Ubuntu 9.10, dump is a pretty standard app, its been around since AT&T unix V6 –  Recursion Nov 24 '09 at 3:40
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2 Answers

up vote 0 down vote accepted

The answer to this question was a corrupt ext3 file system. which caused it to report file size wrong.

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Reading through the man page for dump leads me to believe that there are several reasons that its output might be smaller than expected.

  • how the total size of the files to be backed up is determined and how the size of the output is determined - different utilities differ in the method they use to calculate totals or have options to set different methods
  • an error in specifying what to back up could lead to missing part of what was intended.
  • the type of compression used and the compressibility of the original files (which can vary to a great degree), also what role hardware compression may play
  • whatever differences in storage efficiency exist between ext3 and the output of dump. Ext3 is very efficient so I wouldn't expect a lot of gain here
  • which options are selected and the parameters supplied, for example whether inodes are excluded

When you are talking about a "past level 0" are you asking whether it takes into account the contents of the previous backup and abbreviates the new one? My read of the man page is that "level 0" means a full backup, not an incremental one. So the answer is almost certainly "no".

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