Hashing of files

Something that every so often arises on the (now absent) forum is why DC++ re-hashes some files. People with network drives are among the majority of these users.

There are two reasons why DC++ would (re-)hash a file.
(1) The path to the file has changed. (The file name is included here.)
(2) The file content has changed.

People don’t realize why (1) is important. They think that DC++ could just look at the file name and see “that it’s the same file”. However, this would obviously not work well if you have multiple files named the same (“example.png”) sprinkled through your share.

(2) is obvious if you’re indeed changing the content of a file intentionally. However, there’s some software that “automatically” do this for you. You might experience this the most with MP3 files and documents. Certain media players like to change the ID3 tag of MP3s, and various document editors like to set their own foot print on the files.

People with network shares may see these things regularly. Detaching and re-attaching the network drive may cause them to update the files’ timestamp and may cause DC++ to re-hash the files [2]. Sometimes, the path may also change, causing (1) to happen.

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One Response to Hashing of files

  1. emtee says:

    Thist can happen with external devices as well if once DC++ started with the drive detached and later when it started with the device (containing (a part) of the share) re-attached again.
    Also the (1) case can happen with these removable hdd’s because – unless the user doesn’t make some configuration – the attached drive gets the first available drive letter what can varies time to time if serveral combination of external disks, usb sticks/card readers are used with the same computer. Needless to say this is one of the most annoying thing in Windows…
    To solve the problem it worth to assign a fix drive letter to the external device ( http://support.microsoft.com/?kbid=307844 ) or mount the whole drive to a folder in the local filesystem ( http://support.microsoft.com/kb/307889 )
    The lattter solution requires NTFS file system of course.

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