TimeMachine backups on multiple volumes?
Yes, when you go to the Time Machine preferences, just select Use Both when adding the additional drive.

From: OS X El Capitan: Use multiple backup disks


  Time Machine rotates the backup schedule among the disks. For each disk, Time Machine backs up everything that’s changed since the last time that disk was used. If you designated items that shouldn’t be backed up, the list of excluded items applies to all backup disks.
  
  If you use multiple backup disks, when you click the Time Machine icon  in the menu bar and choose Enter Time Machine, you see the timeline for all the accessible disks used for backing up. To see the timeline for a specific disk, click the Time Machine icon, press the Option key, then choose Browse Other Backup Disks.


Note that there is a similar page for each of the last few major OS X releases too.