Hello. Yesterday I decided to update to Sierra from El Capitan on both the disks on my Macbook Pro (mid 2012); the update on my SSD went without a hitch so I decided I'd update my other disk, too. I downloaded the .app and the installation started as normal; once it got to the point where I'd have to restart, though, the problems started. Once the Mac booted, a folder with a question mark appeared; I read that resetting the VRAM and choosing a startup disk (again?) helps in these cases, and it did; however, now I get a prohibited symbol whenever I try to log in on my hard disk. To be exact, it happens after I insert the login password and the loading bar is almost full. Is there some way to gain back access to the volume, or even just access to the files? I have 100GB+ of Photos Library that I'd really, really like not to lose... Here are some of the things I tried: Basic Fix & Repair Options : from both the terminal and Disk Utility, on both Single User Mode and Recovery Mode. The "Repair" option in Disk Utility, in particular, gives this error: "File system exit code is 8. An internal error has occured". Trying to Mount the volume, in whatever way, has no effect whatsoever or I just get an error that the volume can't be mounted. Also, the partition now shows up as greyed out and called "--" (empty); it was called "Macintosh HD". The name still appears in several other disk utility apps, but still something to note. Recovery Mode : I tried re-installing the OS but the volume is now unmounted so it doesn't show up as a possible option. Also, I found an article saying that booting problems could come from old extensions that no longer work after an update; the article described the terminal steps to take in order to move all non-Apple extensions to a folder on the volume and make it bootable again. However, same problem, the volume is unnamed and unmounted and it doesn't show up anywhere, nor can I "cd" into it. Safe Mode : I can't start Safe Boot into the damaged partition: to load it, I need to hold the Option key and choose it from a list and doing that and holding Shift too doesn't do anything. I can only boot in Safe Mode on my working OS X partition (SSD) and that defeats the purpose. Thinking about it now, is there a way to Safe Boot into a different disk/partition? Single User Mode & fsck : I ran the fsck command (and variations) multiple times on the faulty partition and others, too, and at some point I got a "GRUB.Geom.Hard Disk.Read.Error" or something like that, that as far as I can see now it's been resolved; still, no success on booting the OSX partition. After the fixes, though, an "EFI" partition that wasn't mounted and visible from any OS now suddenly is. It contains a folder called "APPLE" with three more folders inside it: CACHES (one more folder, empty), EXTENSIONS (Firmware.scap) and FIRMWARE (MBP91_00D3_B0C_LOCKED.scap). What are these? VRAM Reset : did nothing. Volume Rebuilding : I've tried using both TechTool Pro and DiskWarrior to rebuild the partition, as both apps signaled damaged volume integrity and structure; neither app was able to rebuild the volume. TechTool Pro, in particular, stops at the very first verification step, "Journaled HFS Plus Volume". Does that mean the volume isn't recognised as HFS+ anymore? Does this have any significance? OS X Combo Updates : The volume, being unmounted, doesn't show up so I can't install anything on that partition. Data Recovery Tools : I tried using Data Rescue 4 and it extracted a bunch of unusable and un-extractable .bz2 and .gz files, size around 10GB. SMC Reset : Will try this one later. This is my partition scheme; the "damaged" volume, on /dev/disk1, has the identifier disk1s2. As you can see, the same disk holds two more partitions, booting Windows 7 and Ubuntu Linux; both are working correctly, so this rules out the hard disk suddenly failing, I guess. Also, several checks of the drive show nothing amiss. The other disk (disk0) is working fine, it's my boot drive and I'm using it right now. Code: /dev/disk0 (internal, physical): #: TYPE NAME SIZE IDENTIFIER 0: GUID_partition_scheme *250.1 GB disk0 1: EFI EFI 209.7 MB disk0s1 2: Apple_HFS Crucial SSD 249.2 GB disk0s2 3: Apple_Boot Recovery HD 650.0 MB disk0s3 /dev/disk1 (internal, physical): #: TYPE NAME SIZE IDENTIFIER 0: GUID_partition_scheme *500.1 GB disk1 1: EFI EFI 209.7 MB disk1s1 2: Apple_HFS 301.2 GB disk1s2 3: Apple_Boot Recovery HD 650.0 MB disk1s3 4: Microsoft Basic Data BOOTCAMP 165.8 GB disk1s4 5: Linux Filesystem 32.2 GB disk1s5 I really hope there is something else I can do to fix this... Would creating an image of the drive save the files? I had been thinking about switching this disk for an SSD and was preparing for that; I backed up both the BOOTCAMP and Linux partitions, so if it can help those can go and be removed, but I thought I'd backup the OSX one after the update... Awaiting ideas... Thank you.