Linked by Thom Holwerda on Mon 2nd Nov 2009 23:20 UTC
ZFS has received built-in deduplication. "Deduplication is the process of eliminating duplicate copies of data. Dedup is generally either file-level, block-level, or byte-level. Chunks of data - files, blocks, or byte ranges - are checksummed using some hash function that uniquely identifies data with very high probability. Chunks of data are remembered in a table of some sort that maps the data's checksum to its storage location and reference count. When you store another copy of existing data, instead of allocating new space on disk, the dedup code just increments the reference count on the existing data. When data is highly replicated, which is typical of backup servers, virtual machine images, and source code repositories, deduplication can reduce space consumption not just by percentages, but by multiples."
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Member since:
2007-03-26
diff <(head -c 100000 file1.avi) <(head -c 100000 file2.avi)
This will compare the first 100000 bytes of file1.avi and file2.avi.
Unfortunately I'm moving house in a couple of days so my DVDs are packed away - thus I can't rip and diff. (though if anyone else is able to perform this test then i'd love to see the results)
....So I'm going to have to take your word on the differences being there.
However, (and going back to deduping for a moment) if understood the article properly, then the credits don't have to by byte for byte exact as the dedup looks at the bytes themselves rather than the whole MB block of bytes.
Thus there only has to be enough similar grouped bytes for a space saving to occure.
So unless MPEG compression uses some kind of random hash to encode it's data, then surely the very fact that the A/V is the same (timestamp or not) must mean that there are SOME similar bytes that can be grouped and indexed?