54 lines
2.0 KiB
ReStructuredText
54 lines
2.0 KiB
ReStructuredText
.. _hashalgo:
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Hash Algorithms
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===============
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.. versionadded:: 0.13.0
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Description
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-----------
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A folder can use one of several available hash algorithms when determining
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changes to files. The algorithms have different properties -- see the table
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below where the differences between the algorithms are highlighted.
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========= ======== ============= ================= ================
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Algorithm Speed Delta Changes Efficient Renames Efficient Copies
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========= ======== ============= ================= ================
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SHA256 Slow Yes Yes **Yes**
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Murmur3 **Fast** Yes Yes No
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========= ======== ============= ================= ================
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Speed:
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This affects the speed with which content can be hashed. A "slow"
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algorithm requires a lot of CPU power, while a "fast" algorithm does not.
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The actual scanning speed may however be limited by the disk's transfer
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rate.
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Delta Changes:
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Indicates whether changes to the contents of a file are transferred
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efficiently. "Yes" means that only the changed blocks are transferred,
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"no" means the whole file must be resent.
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Efficient Renames:
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Indicates whether renaming a file on one device results in a renaming
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operation on another device ("yes"), or whether the renamed file must be
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transferred over the network ("no").
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Efficient Copies:
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Indicates whether a copy of a file on one device results in a local copy
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operation on another device ("yes"), or whether the copy must be
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transferred over the network ("no").
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Changing the Folder Hash Algorithm
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----------------------------------
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The hash algorithm can only be set when a folder is added to the
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configuration, it can not be changed afterwards. To change the hash algorithm
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of a folder it must be removed and then added again with the new hash
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algorithm. This necessarily results in a full (slow) rescan of the folder
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contents.
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The hash algorithm for a given folder must be the same for all devices sharing
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that folder.
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