+scratch directory when creating temporary copies of the files transferred
+on the receiving side. The default behavior is to create each temporary
+file in the same directory as the associated destination file.
+
+This option is most often used when the receiving disk partition does not
+have enough free space to hold a copy of the largest file in the transfer.
+In this case (i.e. when the scratch directory in on a different disk
+partition), rsync will not be able to rename each received temporary file
+over the top of the associated destination file, but instead must copy it
+into place. Rsync does this by copying the file over the top of the
+destination file, which means that the destination file will contain
+truncated data during this copy. If this were not done this way (even if
+the destination file were first removed, the data locally copied to a
+temporary file in the destination directory, and then renamed into place)
+it would be possible for the old file to continue taking up disk space (if
+someone had it open), and thus there might not be enough room to fit the
+new version on the disk at the same time.
+
+If you are using this option for reasons other than a shortage of disk
+space, you may wish to combine it with the bf(--delay-updates) option,
+which will ensure that all copied files get put into subdirectories in the
+destination hierarchy, awaiting the end of the transfer. If you don't
+have enough room to duplicate all the arriving files on the destination
+partition, another way to tell rsync that you aren't overly concerned
+about disk space is to use the bf(--partial-dir) option with a relative
+path; because this tells rsync that it is OK to stash off a copy of a
+single file in a subdir in the destination hierarchy, rsync will use the
+partial-dir as a staging area to bring over the copied file, and then
+rename it into place from there. (Specifying a bf(--partial-dir) with
+an absolute path does not have this side-effect.)