Crisis - formatted efi partition.

[Grant]

On my old mbp i formatted the wrong partition.
The mbp is running snow leopard with win 7 via boot camp.
I had an ext drive connected.
Within windows 7 I formatted the efi partition by mistake, so now the mac os cannot boot.
The partition structures appear intact except the efi partition is formatted as fat32 and is empty.
Under win7 I can see the mac partition and all its files / folders.

Booting from an ext drive containing snow leopard i can also see the files on the mac drive.

How do I fix / repair the efi partition to allow the mbp to boot into the mac os again ?

 

[DJ...]

From what I've read on the forums, as long as you haven't written anything new to the drive, recovery software like Recuva should work? Unless the file system makes a difference and I'm showing my incredibly limited geekery...

 

[vinodh]

Try booting from the Snow Leopard DVD and create a partition large enough to install Snow Leopard. Install Snow Leopard but make sure you leave the original Snow Leopard partition with all you data intact. Boot to your new Snow Leopard desktop, open System Preferences>Target Disk and choose the original Snow Leopard installation ad the default boot OS. Reboot to your old OS and then use Disk Utility to delete the new Snow Leopard partition.

To recap: This method uses a fresh install of Snow Leopard to recreate the EFI partition. This also means that you will have 2 Snow Leopard installations but you won't have any data loss. The builtin Target Disk app allows you to choose which OS to boot from by default and then you can easily delete the unused Snow Leopard installation/partition safely.

 

[sajunky]

Don't let anything to write over, it will decrease chance for successful recovery. What was previous filesystem on this partition? Available tools depends on this answer.

 

[Grant]

The drive is formatted as GUID. The mac partition is HFS & the win7 partition is NTFS.

 

[vinodh]

If you install a second Snow Leopard OS in a separate partition, there won't be any data loss. It's a simple fix without needing extra software or recovery tools.

 

[Grant]

booting into win7, i can see the mac partition + all folders & files.
disk management in win7 displays the following:
disk 0 = the internal drive
disk 1 = the external drive having a snow leopard boot partition


booting into mac on the external drive, disk utility shows the following:

 

[Grant]

If you install a second Snow Leopard OS in a separate partition, there won't be any data loss. It's a simple fix without needing extra software or recovery tools.

i have 2 snow leopard install discs - mbp spits both out (as mbp's superdrives often do with dvd's)
using an external dvd drive, neither will mount on startup (using option key)

booting into snow leopard using the ext hard drive, the discs mount in sidebar when inserted into the ext dvd drive.

 

[Grant]

it seems the mac partition the internal drive is now FAT:


looking at the ext bootable drive i find GUID:


so it would appear the mac partition landed up changing from GUID to FAT without losing any data.

 

[vinodh]

Make a USB Snow Leopard installer. Here's a guide: http://www.techrepublic.com/blog/ap...ow-to-create-a-bootable-usb-to-install-os-x/#.

Boot to the external drive to make the USB installer. Also, while you are there, copy all important files/documents from the unusable Mac partition as a backup.

 

[Grant]

Make a USB Snow Leopard installer. Here's a guide: http://www.techrepublic.com/blog/ap...ow-to-create-a-bootable-usb-to-install-os-x/#.

Boot to the external drive to make the USB installer. Also, while you are there, copy all important files/documents from the unusable Mac partition as a backup.

will give that a try - just have to forage around for a spare drive of flash drive

 

[[)roi(]]

Make sure you have a backup before trying these:
http://apple.stackexchange.com/questions/57597/how-to-fix-broken-efi-partition

http://www.coriolis-systems.com/iPartition.php

 

[jansdejager]

just reinstall snow leopard? afaik it only overwrites system files and keeps your user files intact. But just back them up in case

 

[[)roi(]]

just reinstall snow leopard? afaik it only overwrites system files and keeps your user files intact. But just back them up in case

Typically installs and EFI updates will fail if there's no EFI partition.

 

[vinodh]

Typically installs and EFI updates will fail if there's no EFI partition.

It won't. If the OS is present but the EFI partition is missing/wrong format, then re-installing on top of the existing installation will rewrite the EFI partition and keep all settings and user information. Probably will be the simplest method to fix the OP's problem. Not the cleanest method since it's essentially an upgrade install but will work none the less.

 

[[)roi(]]

It won't. If the OS is present but the EFI partition is missing/wrong format, then re-installing on top of the existing installation will rewrite the EFI partition and keep all settings and user information. Probably will be the simplest method to fix the OP's problem. Not the cleanest method since it's essentially an upgrade install but will work none the less.

Strange, as according to this Lion to ML thread: it's not? http://apple.stackexchange.com/questions/57597/how-to-fix-broken-efi-partition

Also rerunning an install doesn't gelp to correct a problem of a missing recovery partition -- yet that issue can be fixed manually.

 

[jansdejager]

I've done a lot of OSX installs post-snowleopard and I can assure you that you can start from scratch no matter what your hard drive partition table looks like. Not sure if your boot camp setup will survive, but don't see why it wouldn't, assuming you configure it again. try researching refit or other alternative boot loaders for mac. your efi partition is highly configurable and easy to fix compared to bios boot, as long as it's a fat32 partition of 100mb or more as the first partition on your gpt formatted partition table

 

[Grant]

I've done a lot of OSX installs post-snowleopard and I can assure you that you can start from scratch no matter what your hard drive partition table looks like. Not sure if your boot camp setup will survive, but don't see why it wouldn't, assuming you configure it again. try researching refit or other alternative boot loaders for mac. your efi partition is highly configurable and easy to fix compared to bios boot, as long as it's a fat32 partition of 100mb or more as the first partition on your gpt formatted partition table

not at all concerned with the boot camp partition, although at this point I am only able to access files / folders on the mac partition via win7 in boot camp.
i am unable to see the mac partition (or files / folders contained therein) when booting into snow leopard via the external bootable mac drive.
**is there some 3rd party mac program that will read the files / folders on the mac partition ?

as mentioned before, it appears the mac partition (or entire drive) got converted to a MBR system without data loss, boot camp partition remained NTFS as per below:


backing up files contained on the mac partition is becoming problematic with win7 reporting permission errors.

i am sure to be bald by the morning, with the remains of a MBP to be found at the bottom of the swimming pool !


I have also tried to reinstall the mac os. both snow leopard install discs fail to mount on startup (holding option key) using both internal superdrive & external dvd drive.
I tried creating a bootable flash drive containing the osx install, as per instructions in an earlier post - that too failed to boot.

 

[Grant]

I've done a lot of OSX installs post-snowleopard and I can assure you that you can start from scratch no matter what your hard drive partition table looks like. Not sure if your boot camp setup will survive, but don't see why it wouldn't, assuming you configure it again. try researching refit or other alternative boot loaders for mac. your efi partition is highly configurable and easy to fix compared to bios boot, as long as it's a fat32 partition of 100mb or more as the first partition on your gpt formatted partition table

refit was installed, but now no longer accessible.
would refit work if it was installed onto the external drive containing the bootable os

i am assuming it would have to be installed on the primary internal drive

 

[Grant]

So i just woke up having got a call from a mate in london is pretty clued up with mac.
As luck would have it he was minutes from boarding a flight to hong kong, but asked me to send a screenshot of "disk utility".

I was told to open terminal and enter a command regards (do not remember what it was), but was related to "disk0s1" as seen in disk utility.
On entering the command, terminal responded with: "No partition map exists"
He sent this back:


And then he had to board his flight !!!