Carbon Copy Cloner
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Full user review
"Simple and fast backup or cloning"
Cloning is very fast, especially using a USB 3.0 HDD.
None, really, at least none that I have discovered.
I have used CCC for many years in its various forms but always as a cloning aid. I only recently learned that CCC could also perform regular backups. I suppose this oversight is because I mainly use Time Machine.
HDD failure is, thankfully, extremely rare but on the odd occasion I have found myself in trouble, I have resorted to booting from a clone and I have used the diagnostic & repair applications on the clone to repair my main HDD.
CCC has never failed me and I have recommended it to friends because it is both reliable and cheap.
CCC 3.4.1 builds upon previous strengths. Recommended.