diff --git a/draft/hashalgo.rst b/draft/hashalgo.rst new file mode 100644 index 000000000..358b13ed9 --- /dev/null +++ b/draft/hashalgo.rst @@ -0,0 +1,53 @@ +.. _hashalgo: + +Hash Algorithms +=============== + +.. versionadded:: 0.13.0 + +Description +----------- + +A folder can use one of several available hash algorithms when determining +changes to files. The algorithms have different properties -- see the table +below where the differences between the algorithms are highlighted. + +========= ======== ============= ================= ================ +Algorithm Speed Delta Changes Efficient Renames Efficient Copies +========= ======== ============= ================= ================ +SHA256 Slow Yes Yes **Yes** +Murmur3 **Fast** Yes Yes No +========= ======== ============= ================= ================ + +Speed: + This affects the speed with which content can be hashed. A "slow" + algorithm requires a lot of CPU power, while a "fast" algorithm does not. + The actual scanning speed may however be limited by the disk's transfer + rate. + +Delta Changes: + Indicates whether changes to the contents of a file are transferred + efficiently. "Yes" means that only the changed blocks are transferred, + "no" means the whole file must be resent. + +Efficient Renames: + Indicates whether renaming a file on one device results in a renaming + operation on another device ("yes"), or whether the renamed file must be + transferred over the network ("no"). + +Efficient Copies: + Indicates whether a copy of a file on one device results in a local copy + operation on another device ("yes"), or whether the copy must be + transferred over the network ("no"). + +Changing the Folder Hash Algorithm +---------------------------------- + +The hash algorithm can only be set when a folder is added to the +configuration, it can not be changed afterwards. To change the hash algorithm +of a folder it must be removed and then added again with the new hash +algorithm. This necessarily results in a full (slow) rescan of the folder +contents. + +The hash algorithm for a given folder must be the same for all devices sharing +that folder.