laCie Thunderbolt hard drive will not mount after installing 10.9.4

I have a laCie Thunderbolt 6TB hard drive which is exhibiting the same symptom after upgrading after installing 10.12.4. However, in my case I am able to cycle power on the drive and it will be recognized and mount. Any help would be greatly appreciated.

Please read this whole message before doing anything.

This procedure is a diagnostic test. It’s unlikely to solve your problem. Don’t be disappointed when you find that nothing has changed after you complete it.

The purpose of the test is to determine whether the problem is caused by third-party software that loads automatically at startup or login, by a peripheral device, by a font conflict, or by corruption of the file system or of certain system caches.

Disconnect all wired peripherals except those needed for the test, and remove all aftermarket expansion cards, if applicable. Start up in safe mode and log in to the account with the problem. You must hold down the shift key twice: once when you turn on the computer, and again when you log in.

Note: If FileVault is enabled, or if a firmware password is set, or if the startup volume is a Fusion Drive or a software RAID, you can’t do this. Ask for further instructions.

Safe mode is much slower to start up and run than normal, with limited graphics performance, and some things won’t work at all, including sound output and Wi-Fi on certain models. The next normal startup may also be somewhat slow.

The login screen appears even if you usually login automatically. You must know your login password in order to log in. If you’ve forgotten the password, you will need to reset it before you begin.

Test while in safe mode. Same problem?

After testing, restart as usual (not in safe mode) and verify that you still have the problem. Post the results of the test.

I Also have a 4TB LaCie drive that has been unmounting itself every five minutes since installing the 10.9.4 update. I've managed to stop that behavior by switching from the Thunderbolt cable to the USB cable. It's slower, but the drive stays mounted. I'll hope for better with 10.9.5 or Yosemite.

I am having the same problems with the Lacie and both my 30 inch thunderbolt displays flicker on and off sometimes also.

This has been a disaster and I am using the Yosemite and so I warn you not to do it as it only makes the issue worse.

My $1000.00 Lacie does not even have a USB only that Worthless thunderbolt , very sad about the whole issue.

Lacie has not responded as they are waiting for apple to do something and apple is waiting for the thunderbolt technology to fall.

How do they not make sure that thunderbolt technology is working I dont get it. ????

I just purchased an iMac Retina 27" and the LaCie 4TB Thunderbolt external drive for backups. The drive has worked without issue under Yosemite till this afternoon. It would not mount. The USB connection worked and mounted the drive instantly.

I packed the drive up, went to the store and it tested fine on a Mavericks iMac. I came home, plugged in all in again and the 4TB worked. Go figure.

The only change was that this morning I added my old USB LaCie 2TB drive to TimeMachine to use as an off-site back up. I doubt that would be the cause of the issue. The 2TB was switched off when the 4TB issue came up.

The rep in the store suggested it is a software issue (I agree) and so we wait for an update from either Apple or LaCie.

Contact LaCie. It is their product.