Second HDD backup for OS X 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?
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 -&gt; External HDD1 (TM1 + Data)
Macintosh HD -&gt; 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.