PresSTORE Synchronize - Principles of Operation
Posted by Ibrahim Tannir, Last modified by Sven Koester on 17 April 2012 14:38
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For Synchronize, PresSTORE does not keep a permanent index. An index of the folders and files of the source is built on the fly. This index is sent over to the client where the target for the replication resides. The client checks the target folders and files against the index and returns a list of the differences back to the server. The change is determined based upon the file's attributes, but not upon its contents. The attributes include: modification time - mtime, file inode change - ctime, size, Posix permissions, owner, group, extended attributes, ACLs and windows backup flag. Since the contents is not considered, there is consequently no checksum done on the file. When copying the files, PresSTORE will copy all it's parts including Windows streams, Helios, Xinet and NetAtalk resource forks and the extended attributes and ACLs when possible. If the file systems are not compatible, the parts that cannot be copied are left out or converted into a compatible format, as in the case of Apple Double files. ACLs are not copied accross different file and operating systems, ownership and Posix permissions are kept as far as possible. One can choose to encrypt the data during transfer. | |
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Q: Which filesystems have «notifications about any changes» that PresSTORE supports and are they usable when source and target are different file systems?
S: For the case that the volumes are almost full and syncing fails because of target full: Could PresSTORE switch to a special state that it syncs in two passes. Fist pass just deletes what has to be deleted, second pass tries to copy what has to be copied.