Lost partition on hard drive - wont boot

[jwk87]

Hi all,
No idea on how this has happened but have lost the boot partition on my mac drive.

Please see the attached screen shot. The hard drive is disk1. All the files are still there and recovered well.

When it tries to boot I get the folder with the question mark.

Any help on how to change disk1s2 to a bootable Apple_HFS without any data loss would be appreciated.

Thanks

Jason

 

[Lufbrarunner]

Are you able to boot into the recovery partition? (Command +R at startup.)

 

[jwk87]

No there is no recovery partition on this disk.

 

[Cory Cooper]

Hello and welcome.

-Which model iMac?
-Which version of OS X/macOS?
-For clarification, your Mac will still startup from the internal (disk0s2) drive, just not the external (disk1s2), correct?
-If you can startup from the internal disk, does the external disk mount, and can you see any files on it?
-What brand/model is the external, and how is it connected?
-Which version of OS X/macOS was installed on it?
-It looks like you have other disks connected or other , from what I can see on your screenshot, correct?
-Do you have a Time Machine or other backup of the external drive?
-Do you have any utilities like DiskWarrior?

Unfortunately, there isn't a way to change the disk format/partition scheme of a disk without losing all of the data. It could be either some form of disk directory corruption, or the start of disk hardware failure.

C