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    <p>The idea is <em>not</em> to change the file content, but rather its name (and path), by using a hash value.</p> <p>Changing the content with a hash would be disastrous since a hash is normally not reversible.</p> <p>I'm not sure of the motivivation for using a <em>hash</em> rather than the file name (or even rather than a long random number), but here are a few advantages of the hash appraoch:</p> <ul> <li>the file names on the disk is uniform</li> <li>the upper or lower parts of the hash value can be used to name the directories and hence distribute the files relatively uniformely</li> <li>the name becomes a code, making it difficult for someone to a) guess a file name b) categorize pictures (would someone steal the hard drive content)</li> <li>be able to retrieve the filename and location from the file contents itself (assuming the hash comes from such content. (not quite sure which use case would involve this... a bit contrieved...)</li> </ul> <p>The general interest of using a hash is that unlike a file name, a hash is meaningless, and therefore one would require the database to relate images and "bibliographic" type data (name of uploader, date of upload, tags, ...)</p> <p>In thinking about it, re-reading the referenced SO response, I don't really see much of an advantage of a hash, as compared to, say, a random number...</p> <p>Furthermore... some hashes produce a numeric value, typically expressed in hexadecimal (as seen in the refernced SO question) and this could be seen as wasteful, by making the file names longer than they need to be, and hence putting more stress on the file system (bigger directories...)</p>
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    1. POSHA-1 hash for storing Files
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    1. COIf you use hash then several identical copies of the same files are stored to same location. With random number, the files will be stored to different locations. This may be an advantage or disadvantage, depending on your case.
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      1. USJuha Syrjälä
    2. COwhat does someone like flickr or facebook do?
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      1. USLance Pollard
    3. COhere is some interesting information about facebook's photo storage infrastructure http://www.facebook.com/note.php?note_id=76191543919
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