I have a 500 GB Mac and set up Time Machine to do the back up to an external HDD (external hdd 1). All my files are also stored in the external hdd 1.

I would like to have a second external hdd (external hdd 2) backing up the Mac hdd and also the external hdd 1, both via Time Machine. Is that possible? Maybe another option is better?

1 Answer 1


A backup drive is automatically excluded from a Time Machine backup. In your case the nested backup strategy will not work using Time Machine because External HDD1 will be excluded from being backed up to External HDD2:

Macintosh HD -> External HDD1 (TM1 + Data)
Macintosh HD -> External HDD2 (External HDD1 will be excluded)

You may either split External HDD1 into a Data volume and a backup volume (External HDD1-BV) and then backup Macintosh HD + Data to External HDD1-BV/External HDD2 or you have to use another tool to backup External HDD1 to External HDD2.

  • Having Macintosh HD + Data into External HDD2 would be great. I would have to split External HDD1 into a Data volume to do that, right?
    – biotech
    Apr 20, 2016 at 16:54
  • @biotech Yes, External HDD1 has to be split in two volumes: Data and a Time Machine volume (BV). Now it depends on how big the disk is (and the size of Data+Macintosh HD has to be smaller than BV) whether this is possible at all.
    – klanomath
    Apr 20, 2016 at 16:59
  • @biotech Please add the size of your Data folder on External HDD1 and the size of the time machine backup folder as well as the total sizes of External HDD1/2
    – klanomath
    Apr 20, 2016 at 17:03
  • Hi there how it's going. You remember these thread. So now I have trouble. External HDD1 is now broken is not working because I dropped it. So now what should I do to built is external HHD1 from HDD2? Thanks so much @klanomath
    – biotech
    Jun 4, 2016 at 10:37
  • @biotech Please add a new question and mention your actual configuration/apps used.
    – klanomath
    Jun 4, 2016 at 10:40

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