Can't erase my Time Machine drive using Disk Utility

Select the Drive Name, IE the Top Level entry for that external drive then the Partition Tab and repartition as One Partition.

Could be TM is actively accessing the drive so first turn Off TM.

Apple just preventing ignorant users from messing up their backup drive.

TimeMachine has special permissions but I think it can be deleted if you hold option key boot from a 10.6 disk or command r boot from 10.7/10.8 Recovery HD partition and use that Disk Utility instead of the one in your OS X Utilities folder, according to Pondini

http://pondini.org/TM/12.html

Consider bootable clones, they are on a order of a magnitude better in many ways to TimeMachine.

Most commonly used backup methods

Are you on a Macbook Pro Notebook or a Mac Pro Desktop system?

Those drives look to be Internal drives not externals and that is not possible on a MBP notebook. 2 drive yes but 3 physical drives in a Mac notebook, No Way.

Is there also a version of OS X installed on that TM drive? As I would think that the BOOT drive would always show at the top of that list and secondary physical drives below the Boot drive.

Also the TM drive does not have a Drive Manufacturers name or the size listed, which is very odd also. Even if it is designated as a TM backup disk it should still have a manufacturers name and the total size of the drive listed just like the other 2 Physical drives and your External drive.

Now I see it a Logic Volume Group. That is the problem and or Reason you don't get any options. You must first break apart the volume group to actually access the physical disks.

One Tip.

Never ever use and internal disk as a TM backup drive, and along with that never a Volume Group as a TM backup drive.

A Logical Volume Group is a combination of 2 or more physical disks or partitions on different Physical disk made to look like one physical drive. So more then likely you are using one partition on both the SSD and the Hitachi disk combined into that Volume Group.

How and when that was created only you would know or whoever set that system up like that. What you have now, IMHO, is a Cluster Fark and should be wiped out and done differently

I know a method using Linux that would work for sure to erase that disk.

Remove all other drives

If you have a Mac with a Superdrive, then burn a ISO of Parted Magic to disk

http://partedmagic.com/doku.php?id=downloads

1. Insert a blank disc.
2. Start Disk Utility.
3. From the File menu, choose Open Disk Image and select the ISO to be burned.
4. In the list of volumes, you will now see an item representing the ISO file. Select it.
5. Click the Burn button and follow the instructions.

Next you will need to boot from the disk, hold the option key down with the Parted Magic disk inside while booting, it will give a list of options eventually and Parted Magic disk will be there, click the arrow to boot from it.

Leave the screen alone and it should boot into RAM and spit out the disk, so prepare for it.

What you want is GParted, that will do a number on unlocking the drive and reformatting it, thus you can later access it in Disk Utility and format it as you wish.

If your Mac doesn't have a Superdrive, then your going to need to use a Windows machine, BootCamp or Windows ina virtual machine to download PenDrive Linux, which you can install Parted Magic onto a USB thumb drive and then use that to option boot the Mac with.

You also can install Linux Mint into a virtual machine in OS X and use GParted there to unlock the drive.

I'll have to mess around with this later to get a better set of instructions, but one would think there would be a Apple method to do so. Surprised Pondini didn't know, perhaps this is a glitch doing it.

So it's a Filevault encrypted TimeMachine backup? Oh well.

Sorry I didn't read that you had encrypted the TM backup. Are all your drives encrypted? If so you will need to disable that before you can do anything.

If you have a Clone of your Boot drive/partition and you have externals large enough or enought of them I suggest you backup, IE COPY, all your data to those external.

Then you can use the Online Internet Recovery system to Completely erase and or re-partition all of your physical drives in your system and start fresh.

That is possible if you have any Mac computer that originally came from Apple with either Lion or Mt Lion Pre-Installed on it.

If it is a older or even slightly older Mac that came with Snow Leopard or Leopard you can use the original system disc to do the same thing. OS X, any version, will boot from an External DVD drive connected by USB, you don't need to have an internal DVD for OS X to boot from an external DVD drive.

All that Apple will do is either completely erase ALL DRIVES in your system and reinstall the originally included version of OS X or they Will Say NO we will not work on it as it has been modified in a way Apple does not approve of because of the second HDD in the optical bay.

Also in the future, IE as soon as you get this straightened out, do not store TM backups on any internal drive/disk. you should always use an external drive for that whether connected by USB, Firewire, Thunderbolt or a Networked NAS system like an Apple Time Capsule.

Storing TM backups on an internal drive/disk is just asking for trouble if the system should fail in some way.

WhyGuy wrote:

I don't know why it has an internal disk icon.

The generic default is the internal looking graphic likely as it doesn't store information in plain to use a graphic like a external drive icon, which would be stored on it to identify different drives and makes.

Then it must be the enclosure you are using those 2 drives in. It setup some type of logical storage volume between those 2 physical disks installed in side of it.

As to the drive icon this is a Firewire enclosure and Mac OS X may use the generic disk icon for FW connected drives. FW is also seen as a network resource as it shows up in both Mac and Windows in the network setting area.

WhyGuy wrote:

That's whats's so strange. The TIme Machine backup is external. I don't know why it has an internal disk icon.

I have a dual slot OWC Firewire External Drive enclosure with a 1 TB physical disk alloctaed to time machine and a second 500 GB physcial drive (in the same external firewire enclousre) for my redundant bootable clone backup using Super Duper.

WhyGuy wrote:

. . .

I have no idea why Time Machine is showing up as an internal drive.

Disk Utility does that on encrypted drives, even externals (why, I have no clue).

I haven't done this in a while, so bear with me. As I recall, you need to select the partition (indented); then the the Mount or icon will be enabled. When you click it, you'll get a prompt for the encryption password, and can then erase the partition. If you change the format to a non-encrypted format, the icon will return to a normal external HD.