I have 2; 2 terabyte western digital hard drives that I use to store all my music content on, including an itunes library. I have albums ripped in flac, & in mp3. I also scan my album art & have separate folders for these scans. my hard drives are labeled; MUSIC 2TB-A, & the backup is MUSIC 2TB-B. I have been using disc utility on my mac to do the backup. In the restore tab, i drag the music drive A into the source space, & the music drive B into the target space. I choose erase destination & replace with contents of A, except for what is only on B or something like this. I have been going through scanning & ripping all my audio Cd's, & updating/browsing my drive A & I am finding that albums that I ripped & remember scanning album art, is missing, I either find the ripped album, & missing the scan, or I have the scans but am missing the album. It is odd because before I did my last backup of drive A to B, I remember seeing the missing items that were on drive A. And after that backup, they are gone. Either way, it is getting a bit tedious in that I am gong back & redoing things, & I do distinctly remember scanning or ripping the albums, where things are missing. I am also or try to be careful about what I delete. Is there something or setting that I am not getting? maybe i need to do a complete format & erase of the B music drive each time before I back it up/copy with music drive A contents to start fresh? so far, I just did the format of drive B the 1st time I connected it to disk utility, & all the subsequent backups I have done to it (for each time I add more to the A drive) I have used the restore function to copy. I have not done an erase or format 1st before I connect & restore/copy drive A onto drive B. Is there a fairly simple way I can do a backup between hard drives on either a mac or PC, & be sure that drive B is exactly like drive A, so I do not go back browsing drive A to find things missing?