Time machine excludes second backup hard drive

Time machine can only back up drives that are working properly and Mac-Formatted.

Re: Mac formatted

Drives like the MyBook came with software, and the manufacturer suggested you install that software.

What that software does is to "spare you the annoyance of having to re-initialize the drive" from its factory set Windows New Technology File System (NTFS, the W is silent because there are no other Operating Systems) or similar unusual (on a Mac) format. Instead, the software they provided would simulate a MacOS drive inside an NTFS file for your Mac.

The downside of using the manufacturer's software is that if the manufacturer's software is not loaded, the Macintosh Volume may not be readable, or may not be writable. This means that in startup manager, Installer, and in Recovery such as after a data loss, the Macintosh Volume may not be visible.

The standard advice given here to all users, including novice users, is to discard the manufacturers software and NEVER use it. "Best Practice" is to erase the physical device when new, using only MacOS Disk Utility, and create the fundamental data structures needed for consistent, reliable use by MacOS.

Be sure to "show all devices" which will allow you to ERASE the entire Physical Device by its immutable manufacturer-given device-name, not just user created Volume-name such as ‘Macintosh HD’.

diskutil list

/dev/disk6 (internal, physical):

#: TYPE NAME SIZE IDENTIFIER

0: GUID_partition_scheme *240.1 GB disk6

1: EFI ⁨EFI⁩ 209.7 MB disk6s1

2: Apple_APFS ⁨Container disk7⁩ 239.8 GB disk6s2

/dev/disk7 (synthesized):

#: TYPE NAME SIZE IDENTIFIER

0: APFS Container Scheme - +239.8 GB disk7

Physical Store disk6s2

1: APFS Volume ⁨X14-SSD240⁩ 97.5 GB disk7s1

2: APFS Volume ⁨Preboot⁩ 26.5 MB disk7s2

3: APFS Volume ⁨Recovery⁩ 507.6 MB disk7s3

4: APFS Volume ⁨VM⁩ 20.5 KB disk7s4

Have you done a restart lately?

if not, that is something easy to try.

It thinks the Time capsule drive is still associated, showing the icon for a shared network backup destination. But for some reason has not made a backup in about ten days.

It thinks that LaCie backup drive is still associated, showing the icon for a local time machine backup destination. it has at least one backup on it, but has not made a backup in about 12 days. It has a problem (as indicated by the red dot.) What error message do you get when you click the red dot?

can you photograph or screenshot that pane, and post the image here?

After a Restart, choose "Back Up now" from the time machine menu Icon on the menubar.

what is the status shown in Settings/Prefs > Time machine?

mine shows two locally-attached backup drives that will alternate (every-other Backup goes to every-other drive) and recent (for when the screenshot was taken) backups completed without errors.

So you are saying it used to get backed up, but no longer?

Are you certain it was getting backed up before? is it possible you just never noticed?

In Finder, if you GetInfo on the Drive icon, it will reveal its drive-type:

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