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Following @Édouard's comment I tried booting in verbose mode using command+v at startup. It seems that fsck_hfs is caught in a loop "repairing" and rechecking the drive, which it does 3-4 times before the machine gives up and powers down (see picture 1). The line /dev/rdisk1s2 (NO WRITE) catches my attention. Could this why fsck is unable to make the necessary changes to repair the drive?

Following @Édouard's comment I tried booting in verbose mode using command+v at startup. It seems that fsck_hfs is caught in a loop "repairing" and rechecking the drive, which it does 3-4 times before the machine gives up and powers down (see picture 1). The line /dev/rdisk1s2 (NO WRITE) catches my attention. Could this be why fsck is unable to make the necessary changes to repair the drive?

Following @Édouard's comment I tried booting in verbose mode using command+v at startup. It seems that fsck_hfs is caught in a loop "repairing" and rechecking the drive, which it does 3-4 times before the machine gives up and powers down (see picture 1). The line /dev/rdisk1s2 (NO WRITE) catches my attention. Could this why fsck is unable to make the necessary changes to repair the drive? I agree that it certainly smells like a bad disk.

Following @Édouard's comment I tried booting in verbose mode using command+v at startup. It seems that fsck_hfs is caught in a loop "repairing" and rechecking the drive, which it does 3-4 times before the machine gives up and powers down (see picture 1). The line /dev/rdisk1s2 (NO WRITE) catches my attention. Could this why fsck is unable to make the necessary changes to repair the drive?

1. Reboot into recovery using cmd+r. This works and I'm able to launch the Disk Utility. This shows S.M.A.R.T Status : Verified. Running Verify Disk on the HDD (topmost level of the tree) shows no errors. However, running verify on the Macintosh HD partition does show errors and asks me to run Repair Disk, which tells me I have irreparable errors and suggests that I back up my data and reformat.

2. Reformat. Still in recovery mode Disk Utility, I first tried running Erase under the Erase tab on

3. the HDD, resulting in: Disk Erase failed with the error: Couldn't unmount disk. (in retrospect this makes sense because initially I was booting to the recovery partition on the same disk)

4. the Macintosh HD partition, resulting in: Couldn't open disk.

EDIT Following @chillin's suggestion I tried booting to a Mavericks USB install disk, created following the instructions here. Holding option on startup I'm able to select the USB and boot appears normal, but with the same result that I am unable to unmount the internal disk to format, even using diskutil unmountDisk force disk1 (I get the same error messages for all methods described above). I do notice that the option to reinstall OS X has been replaced by an option to install, so I am confident that I'm actually booting to USB.

1. Reboot into recovery using command+r. This works and I'm able to launch the Disk Utility. This shows S.M.A.R.T Status : Verified. Running Verify Disk on the HDD (topmost level of the tree) shows no errors. However, running verify on the Macintosh HD partition does show errors and asks me to run Repair Disk, which tells me I have irreparable errors and suggests that I back up my data and reformat.

2. Reformat. Still in recovery mode Disk Utility, I first tried running Erase under the Erase tab on

3. the HDD, resulting in: Disk Erase failed with the error: Couldn't unmount disk. (in retrospect this makes sense because initially I was booting to the recovery partition on the same disk)

4. the Macintosh HD partition, resulting in: Couldn't open disk.

EDIT

Following @chillin's suggestion I tried booting to a Mavericks USB install disk, created following the instructions here. Holding option on startup I'm able to select the USB and boot appears normal, but with the same result that I am unable to unmount the internal disk to format, even using diskutil unmountDisk force disk1 (I get the same error messages for all methods described above). I do notice that the option to reinstall OS X has been replaced by an option to install, so I am confident that I'm actually booting to USB.

###EDIT 2

Following @Édouard's comment I tried booting in verbose mode using command+v at startup. It seems that fsck_hfs is caught in a loop "repairing" and rechecking the drive, which it does 3-4 times before the machine gives up and powers down (see picture 1). The line /dev/rdisk1s2 (NO WRITE) catches my attention. Could this why fsck is unable to make the necessary changes to repair the drive? I agree that it certainly smells like a bad disk.