iMac with Tahoe not prompting password for external LaCie drive

There were a few prior posts on this forum from users who couldn’t access their external drive due to the drive manufacturer’s software that they used to encrypt the drive. Lacie/Seagate, Samsung, SanDisk, etc., all provide 'drive management' software on their drives and using such 3rd party software can cause issues when macOS is updated and the 3rd party software becomes incompatible. Not sure if that's the issue here, but FYI the best practice with a new external drive (SSD/HDD, not applicable to NAS drives) is to use Disk Utility to complete erase it, format it as GUID/APFS and apply encryption if desired.

If you set the drive up 'properly' (by erasing it, setting it up as a new, encrypted drive in Disk Utility), and are not seeing a password prompt, this typically happens when you open the disk image, are prompted to enter the password and tick the box to save the password in your keychain. The disk is still encrypted, but Keychain provides the password when you open it.

Two options at this point:

Create a new encrypted disk image in Disk Utility, copy the contents from the old one to the new one then delete the old one. Be careful to not tick the save password box at any time when entering the password.

—OR—

Delete the password for the disk from your Keychain. You won't find it in the Passwords app, and since that app was launched, Apple has buried Keychain Access...but it's still there. Easiest to just do a Spotlight search for Keychain Access (or you can navigate to it in System/Library/CoreServices/Applications). When prompted, choose the non-default option to open Keychain Access instead of Passwords.

You should find the password somewhere in the Login keychain, you can search by the name of the drive. Delete the entry and next time you open the drive, you'll be prompted for the password. Again, be careful to not tick the save password box at any time when entering the password.

Sleighride wrote:

I clicked on the keychain item for "local storage."

Why? Did you name your Time Machine backup "local storage"? Note that localstorage (no space) appears to be a macOS application password used by the Find My app, related to the locating friends functionality. macOS is not letting you access it because you're not supposed to access it.

The password for your external drive will be an entry with the Name of your external drive. For example, my Time Machine backups are to an NAS (primary) and a pair of 4 TB SSDs (secondary, with one swapped offsite weekly). They all have TMB in the name of the backup volume. When I search for 'TMB' in the Keychain Access app, I see this:

If I delete one of those passwords (secondary click aka right click and select Delete), the next time I connect the disk I'll be prompted for the password.

Sleighride wrote:

Concerning Option 2, ..........This is above my pay grade, but why would deleting the current valid password from Keychain prompt Tahoe to ask me for the password?

When you save passwords in the KeyChain/Passwords app, macOS will automatically provide the password when the system needs it. By removing the entry from the KeyChain/Passwords app, the system can no longer automatically unlock the device so it will once more prompt the user to enter the proper credentials.

FYI, you should be able to see the stored password as well when viewing the record in the KeyChain/Passwords app. Probably a good idea to make note of it just to be safe. Maybe the stored password is incorrect, but it doesn't hurt to record just in case you have forgotten the password since it has been automated for a bit.

Understand about erasing the drive at this point, the intent of that was what you should do with a brand new drive, namely don’t use whatever software the manufacturer preloads on the drive. If you did that, the problem may be that software is not compatible with Tahoe in which case check the manufacturers website for an update.

If you stored the password in the Keychain, it won’t ask for it. If you didn’t, it asks. Basically when the disk mounts, macOS checks the Keychain for a stored password and if there isn’t one, it prompts you to enter it. Deleting the saved password restores it to that state.

Sleighride wrote:

... a LaCie Rugged 4 TB USB-C drive. I elected to protect the drive with a password.

You never responded to neuroanatomist about whether you were using a third party disk utility (often provided by companies like LaCie) to set up and manage the encryption on your external drive. If you were using such a utility and it was not updated before you moved to Tahoe, there is a chance that the older version of the disk software is not compatible with Tahoe. In which case the drive might malfunction or in worst case you would lose access to it.

I am reluctant to erase the drive because it may contain old files that are stored nowhere else.

If you get your problem solved without having to erase the drive you should bring those important files in the Time Machine back to your new iMac drive so they will be current in the backups from then on. Also it would be wise to get another external drive and use Carbon Copy Cloner to clone/backup your drive to the eternal drive. I't always wise to have 2 backups of your user data. It won't be able to backup the system however. Time Machine also does not backup the system.