Specifically, when copies are made from/to local filesystems, rsync assumes the -whole-file option. This tool can be used to synchronize devices where space is limited.Īs becomes clear from answer, this implies that -inplace is using the same storage space, but it may still copy the whole file into that space. Instead of using temporary space, the changes to the target file take place in the space already occupied by the current version. We have modified rsync so that it performs file synchronization tasks with in-place reconstruction. So this appears to be the technical details of what rsync -inplace is doing. Representation of a file in a graph, which is then topologically The in-place rsync algorithm encodes the compressed Synchronizing files on cellular phones and handheld PCs, which have Storage for both the old and new version of the file. Space-constrainedĭevices cannot use traditional rsync because it requires memory or Storage the current version of the file occupies. Files on the target host are updated in the same We modified the existing rsync implementation to supportĪbstract: We have modified rsync so that it operates on spaceĬonstrained devices. USENIX Annual Technical Conference, FREENIX track, 91-100, USENIX, 2003. In-Place Rsync: File Synchronization for Mobile and Wireless Devices. The theoretical work on in-place rsync is described in this paper. On the other hand, across a network -no-whole-file is assumed, so -inplace on its own will behave as -inplace -no-whole-file. Note (see comments) that for local filesystems, -whole-file is assumed (see the man page for rsync). You could use strace to further verify if any of the file was written, but this shows it at least used delta-transfer. Sent 494 bytes received 595 bytes 2178.00 bytes/sec $ rsync -av -inplace -no-whole-file a/ b/ Try again with -no-whole-file $ touch a/1 You can verify it re-used the inode with "ls -li", but notice it sent a whole 64K bytes. Sent 65662 bytes received 31 bytes 131386.00 bytes/sec Then touch a file and re-sync $ touch a/1 You also get delta-transfer if you requested '-c'. So, what you're looking for is -no-whole-file, in addition to -inplace. If it doesn't calculate the changes, there won't be block-level changes for btrfs to observe. Rsync assumes that it can write a completely new file and unlink the old one faster than reading both and calculating the changed blocks. If you pass rsync two local paths, it will default to using "-whole-file", and not delta-transfer. TL DR - You need option -inplace and if copying between local filesystems you also need -no-whole-file.
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