-dit(bf(--compare-dest=DIR)) This option instructs rsync to use DIR on
-the destination machine as an additional directory to compare destination
-files against when doing transfers if the files are missing in the
-destination directory. This is useful for doing transfers to a new
-destination while leaving existing files intact, and then doing a
-flash-cutover when all files have been successfully transferred (for
-example by moving directories around and removing the old directory,
-although this skips files that haven't changed; see also --link-dest).
-This option increases the usefulness of --partial because partially
-transferred files will remain in the new temporary destination until they
-have a chance to be completed. If DIR is a relative path, it is relative
-to the destination directory.
-
-dit(bf(--link-dest=DIR)) This option behaves like bf(--compare-dest) but
-also will create hard links from em(DIR) to the destination directory for
-unchanged files. Files with changed ownership or permissions will not be
-linked.
+dit(bf(--compare-dest=DIR)) This option instructs rsync to use em(DIR) on
+the destination machine as an additional hierarchy to compare destination
+files against doing transfers (if the files are missing in the destination
+directory). If a file is found in em(DIR) that is identical to the
+sender's file, the file will NOT be transferred to the destination
+directory. This is useful for creating a sparse backup of just files that
+have changed from an earlier backup.
+
+Beginning in version 2.6.4, multiple --compare-dest directories may be
+provided and rsync will search the list in the order specified until it
+finds an existing file. That first discovery is used as the basis file,
+and also determines if the transfer needs to happen.
+
+If em(DIR) is a relative path, it is relative to the destination directory.
+See also --copy-dest and --link-dest.
+
+dit(bf(--copy-dest=DIR)) This option behaves like bf(--compare-dest), but
+rsync will also copy unchanged files found in em(DIR) to the destination
+directory (using the data in the em(DIR) for an efficient copy). This is
+useful for doing transfers to a new destination while leaving existing
+files intact, and then doing a flash-cutover when all files have been
+successfully transferred.
+
+If em(DIR) is a relative path, it is relative to the destination directory.
+See also --compare-dest and --link-dest.
+
+dit(bf(--link-dest=DIR)) This option behaves like bf(--copy-dest), but
+unchanged files are hard linked from em(DIR) to the destination directory.
+The files must be identical in all preserved attributes (e.g. permissions,
+possibly ownership) in order for the files to be linked together.
+An example:
+
+verb(
+ rsync -av --link-dest=$PWD/prior_dir host:src_dir/ new_dir/
+)
+
+Beginning with version 2.6.4, if more than one --link-dest option is
+specified, rsync will try to find an exact match to link with (searching
+the list in the order specified), and if not found, a basis file from one
+of the em(DIR)s will be selected to try to speed up the transfer.
+
+If em(DIR) is a relative path, it is relative to the destination directory.
+See also --compare-dest and --copy-dest.
+
+Note that rsync versions prior to 2.6.1 had a bug that could prevent
+--link-dest from working properly for a non-root user when -o was specified
+(or implied by -a). You can work-around this bug by avoiding the -o option
+when sending to an old rsync.