Forum Question: Time Machine and cloning HDD

I’m a little confused about the difference between Time Machine backups and cloning my hard drive. Could you explain to me what people mean when they say they have a separate external disk for Time MAchine backups and a separate external disk/partition for a bootable clone?

Comments: 4 Responses to “Time Machine and cloning HDD”

    1/25/11 @ 7:53 am

    A clone is an exact copy of your drive. If you have 10,000 files on your drive, the clone will have 10,000 files — the exact same ones.
    Time Machine creates incremental backups. So it starts by copying those 10,000 files. Then the next hour it notices that you have changed 3 of those files. So now it has the most recent copies of those 3 files, plus the hour-old copies. You can go “back in time” to look at the current copies or the old copies. If you change a file every day for the last 10 days, you will have 10 copies of those files and can go back to any one. As long as you still have space on the TM drive, you can save more and more old copies of files. Eventually very old ones are removed to make room for new ones. But the idea is that you can mess up or delete a file and then go back and get a previous version in most cases.
    Cloned drives used to be cool because you can lose your main hard drive and then boot from the clone and get back up and running fast. But unless that clone is very recent — in the last hour or so — it will be older than the TM backup and it will be worth restoring the TM backup instead. So clones are as useful anymore.
    I only keep a clone so I can store it off-site. I don’t care if it is bootable anymore, and I would only need it if I lost both my drive and my TM drive at the same time (fire, theft, flood, whatever).

    Tim P
    5/23/11 @ 9:26 pm

    I have Time Machine backing up to an external HDD that I use for nothing else but Time Machine. I like your idea of cloning a second backup to a second external HDD to keep off site. Can I use Carbon Copy Cloner (or similar software) to make the cloned backup while still using Time Machine? Will the “flags” left by Time Machine on which files to copy interfere with the “flags” left by Carbon Copy on which files it needs to copy? In other words, can Time Machine and the third party clone software both perform without interfering with each other as to which changed files need to be copied for backup? Thank you.

      5/24/11 @ 6:42 am

      You can use CCC and Time Machine at the same time, yes. No flags are left by either, as far as I know. Time Machine keeps track of its own data on its own drive, and CCC doesn’t need to, I’m pretty sure. It just compares on the fly.
      I do this, but with SuperDuper rather than CCC and have been doing so for years.

    Tim P
    5/24/11 @ 1:08 pm

    Thank you.

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