Chosen Solution
EMC number: EMC 2834 I know enough to know enough, and thats not much.My iMac crashed randomly after upgrading from High Sierra. I can boot into recovery mode but not safe mode. In recovery mode it shows no drive to restart, back up from my time machine, etc. I ran Disk-aid and everything says its fine. If I go to wipe it, it states error can’t write last sector. If I hook it to another iMac and boot it into drive mode it shows only the 128g drive. Thus, it’s safe to assume the Hard Drive has failed in my Fusion Drive set that failed ?? I can’t seem to find a straight answer online, some places say its impossible to work on the drive, etc. A - Is there anything else a novice can do, i’ve accepted the drive is toast but i’m surprised I can’t do anything other than just replace it. B - Is my model capable of me just replacing the hard drive? C - I just ordered a new iMac, so I don’t need a $600 3 TB SSD replacement drive, i’m fine putting in a standard drive. D - My iFixit tool kit just arrived E - What drive works in this computer, F - What glue, gasket, heat tape etc kit do I need. My dad was a computer programmer for Apple for years, I know the lingo to a degree and have enough confidence to crack the Mac open. What I lack is the knowledge to order the right parts and decipher all the forums, info etc.
Hi I’m sorry to hear about your iMac hopefully my answer can help I’ve done a little research and it doesn’t seem like you cant just replace the hdd part of a fusion drive however I would replace the fusion drive with a solid state drive made by intel,Toshiba or Samsung because as far as I know ssd’s are faster that fusion drives If you do want to replace it Here is a video link that give a rough idea of what you have to do https://youtu.be/1YO46G5rifM As for doing the replacement ifixit probably has a tutorial on it Ps if you do replace it please be careful of the exposed power supply as they are extremely dangerous if touched Any questions please ask Thanks:)
Well the good news is you can fix your system! Lets review what a Fusion Drive is as it often confuses people! It is two physical drives, a HDD which is the main drive and a small SSD which is strictly a cache drive. Both your systems ports HDD - SATA connection & SSD - NVMe/PCIe slot are used. The HDD holds ALL of your data! The SSD is like a pony express way station offering a fresh horse for the rest of the run. Here the Cache Drive holds more frequently requested data blocks (that fresh Horse) but the alteration of these data blocks are written back the the HDD. But lets look a bit deeper what are these blocks?? You just started your system so what’s being loaded the OS and if you have already enable auto load of anything that too will be grabbed from the drive. Depending on the size of the cache drive (Apple offered a few different sizes across the different models) once the drive is full thats what is held. Now most of this stuff is not getting altered, but if you don’t auto load then the application you use and its data is more likely to be loaded. Lets say its your 100+ page essay your history teacher is expecting! Well that full document will be held in the cache, but as you correct and polish the document the data blocks get written back, In addition Apple was smart always writing back every so often and lastly iCloud if you have it enabled! OK, Bang! The screen goes wacky and as you discovered the HDD died! So the more important drive of the pair went on you so sadly the data it held is gone! But you where good! You backed up often as you knew HDD’s wear out! Now the tricky part replacing the HDD. Frankly its not overly hard to do! iMac Intel 27" Retina 5K Display Hard Drive Replacement iFixit offers a kit with all of the needed stuff! Or you can replace your drive as you want maybe you want another HDD larger maybe or you want a different vendors drive than what Apple used. You’ll need the iMac Intel 27" (2012-2019) Adhesive Strips and the tool that comes with it BEFORE you start. Unless you have some cardboard to make your own wedge you might as well get this iMac Intel 27" Cardboard Service Wedge. OK what about that sensor thing?? iMac Intel 21.5" and 27" (Late 2012-Late 2015) SSD Temperature Sensor You didn’t tell us which macOS you upgraded to. The reason why this would be helpful is Mojave and newer now use the newer S.M.A.R.T. method of temperature monitoring, you see your systems heat management system (SMC) requires access to the drives sensor and of course Apple contracted for a custom HDD so the internal sensor is exposed for their SMC services. 3rd party drives don’t offer this modification so SMC goes crazy! Slowing your systems CPU clocking to a crawl and ramping up the Fans RPM to protect your system, To be safe I would put it in. Now the last install issue If you are replacing the drive for a 2.5” unit you’ll need an adapter frame. But… What about that cache drive?? You’ll need to wipe it down if you want to create the Fusion Drive again. Remember this only works effectively with a HDD as its mate! Frankly if you want to push your system to the max I would replace the small cache drive with something bigger like 512 GB or 1 TB and making it the boot drive. Here’s the guide iMac Intel 27" Retina 5K Display Blade SSD Replacement Consider just going with the blade drive pulling both Fusion Drive set drives!
Hi Dan, I have the same issue as the OP and had a followup question to your very informative post. Instead of upgrading the blade drive to replace the Fusion Drive set (HDD+Blade), is it possible to just install the HDD with an SSD and somehow disable the use of the blade drive cache? I’m sure an SSD boot drive will be more than enough for me, and it is much easier from what I can tell, to upgrade the HDD than it is the blade drive.
