CMD Reader (05-2106 release) by L.A. Style of the Genesis Project is a backup program for CMD Hard Drive Partitions.  With this program you can copy a backup a CMD partition on Your C64 to a UIEC/SD or other SD2IEC device as a .DNP file which is mountable if your device has a newer firmware (think 0.10.3 or newer).  A 16 meg partition takes about 5 hours with Jiffy DOS.  Although that seems like a long time, it's worth the piece of mind and ease of use.  Just start it and go to bed.