Note on using cpdup with HAMMER1 snapshots

[Matthew Dillon]

    Just a side note here on using cpdup with snapshots, as it has been
    brought up a few times on IRC and in bug reports.

    HAMMER1 snapshots do not have reliable mtime's, because mtime updates
    are not snapshotted.  This can throw cpdup off so my recommendation for
    anyone doing a cpdup from a snapshot to a target which already exists
    is to *ALWAYS* use the -VV option to cpdup.  Note the uppercase.

    The -VV option tells cpdup to ignore mtime entirely and to verify two
    seemingly identical files by actuallying comparing them before deciding
    whether to copy it or not.  It won't be incremental this way since it
    has to read the entirety of the source and target trees, but it will
    still avoid unnecessary writing to the media (good if the target is a
    SSD), and will result in a reliable copy when the source is a HAMMER1
    snapshot.

						-Matt