Archive two drives

In TM preferences select the backup drive. Do not exclude either of the other drives. TM will backup both of them automatically. You don't have to do anything more.

ProfWhiplash wrote:
Automatic back-up of both was my assumption, however that was not the case. It only backs-up the system drive. I double checked my preferences and no drives or files are excluded. The other internal drive does not show up for "exclusion" or otherwise.

When you go to TM Preferences > Options, click the plus sign at the lower right, then your computer's name in the sidebar, does the 2nd internal appear at all?

Or is it shown, but grayed-out?

If it doesn't appear at all, does it appear in the sidebar of Disk Utility (in your Applications/Utilities folder)?

If it does appear in Disk Utility, select the top line, with the make and size. Towards the bottom, the *Partition Map Scheme* should be GUID for an Intel Mac, or +Apple Partition Map+ for a PPC Mac.

Select the line for the partition (indented, with the name). Towards the bottom, the Format should be +Mac OS Exended (Journaled).+

If either is wrong, post what they are.

I read your post on backing up multiple drives in Time machine and all my externals check out by your description but the drives are grayed out and not selectable in Time machine?

Kerkom wrote:
I read your post on backing up multiple drives in Time machine and all my externals check out by your description but the drives are grayed out and not selectable in Time machine?

They are almost certainly not formatted properly for TM to back them up. Were they previously used on Windoze? If so, that's likely the reason.

Use Disk Utility (in your Applications/Utilities folder). Click on the second line of each drive. Down towards the bottom will be listed Format: That must be one of the variants of +Mac OS Extended.+ And for best results with TM, it should be exactly the same as the format of your internal HD and TM drives.

The reason for that is, on a Mac OS Extended partition, but not other formats such as are used on Windoze, OSX keeps a hidden log of all the changes to that disk, which TM then uses to determine what's changed since the last backup and needs to be copied to the TM volume.

Unfortunately, you cannot change the format without erasing.