Chosen Solution
Please help to recover data… as I do not have a back up iMac 27” late 2012 high Sierra Failed to start with internal HDD Booted with OS on USB external disk Ran disk utility first aid to check internal HDD Results below: Volume “Macintosh HD” Repairing file system.Volume is already unmounted.Performing fsck_hfs -fy -x /dev/rdisk0s2Checking Journaled HFS Plus volume.Checking extents overflow file.Checking catalog file.The volume Macintosh HD could not be verified completely.File system check exit code is 8.Restoring the original state found as unmounted.File system verify or repair failed. Volume “Govind’s” Repairing file system.Volume was successfully unmounted.Performing fsck_hfs -fy -x /dev/rdisk0s4Checking Journaled HFS Plus volume.Checking extents overflow file.Checking catalog file.Invalid index keyMissing thread record (id = 519201)Incorrect block count for file 2018.09.18.G80.asl(It should be 85 instead of 79)The volume Govind’s could not be verified completely.File system check exit code is 8.Restoring the original state found as mounted.Problem -69842 occurred while restoring the original mount state.File system verify or repair failed.Operation failed…
It sounds like you’re disk has got physical surface defects. File system repair utilities are of limited use in such cases. Take a look at Advanced Hard Disk Tools in the Restarters Wiki. Unless you can boot your iMac into Linux and DOS utilities (I don’t know whether that’s possible) you’ll need to take out the hard disk and temporarily attach it to a PC. There are 2 possibilities: Spinrite can often recover unreadable sectors by doing its own error correction on the aggregate data accumulated from many reads. It’s far more persistent than any OS or the drive’s internal error recovery logic. If it succeeds it’ll remap the sector. If it was a transient error from a physical jolt or a voltage spike during a write and the disk is otherwise in good health, you can continue using it. However, Spinrite costs $89, but you get a lifetime personal licence and a money back guarantee if it disappoints. If you can boot into Linux of any flavour then ddrescue will clone your hard disc to another. In a first pass it’ll read everything it can and keep a log of any sectors it couldn’t. You can then rerun it as many times as you like and it’ll just retry the sectors it has so far failed to read. This is a good option if you fear your disk is could die completely at any moment, allowing you to recover as much data as possible while you can. After the first run, running Spinrite might well enable it to succeed completely on a second pass. Or, you could just find a professional data recovery firm. For a 3-figure sum they should be able to get your data back if it’s humanly possible, and should only charge if they succeed.
At this point I think you’ll need to use a more powerful tool like Drive Genius to fix your HDD or SSD. I would recommend you not create partitions on your drive. While I know this can be helpful to segragate files it makes space management harder and often wasteful! I would encourage you to think about adding a second drive I’m assuming you have a HDD presently. Your system does have the blade SSD connector so you could add it. Do keep in mind this is a big job but it will offer better performance!
