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Hi, thanks for the answer. How about if the Apple Blade SSD in your Fusion Drive broke and can’t be detected anymore by Disk Util or by Terminal (using diskutil list). What’s the proper way to replace it with a new Apple Blade SSD if the hardisk’s still “fused” to the old Apple SSD? I’m actually OK with the SSD and Hard Disk being split, as long the Late 2015 5K iMac can detect the new Apple SSD (fusing it again as a Fusion Drive would just be a bonus). Is there any hope (pray & fast), that my Apple SSD may not be dead. Fusion destroyed by EaseUS resize. For 7 days, I’ve tried (from 4am to 11pm usually w/other errands and breaks), fusing them again to get them back to normal coz’ it might hinder the upgrade as what happened here in this thread, coz’ the Hard Disk was still fused to the old SSD. Trying everything (reset SMC/PRAM, Safe mode, Internet Recovery, Hardware Diagnostics which was fine - no issues, etc.) to make macOS see the Apple SSD so I can do the diskutil resetFusion command. Windows tools like Disk Management, Device Manager and DiskPart could see an unknown, meaning, no description, called Disk 1. Could this be the Apple SSD? 4 Windows tools/apps detected it, but EaseUS and HardwareInfo did. If anyone has a Late 2015 iMac with Fusion drive, with Boot Camp perhaps you can check if Disk 1 is indeed the Apple Blade SSD. What do you think should I do next, please advise. God bless,
You maybe chasing your tail here! Fusion Drives are an odd duck, The visible size in the OS is just the spinning rust drive (HDD) the solid state drive (SSD) is only acting as a cache drive to the HDD. As such its not seen at the OS level, Disk Utility will see it if you are viewing Show All Devices as seen here
You won’t see its content as its not in a file format, its based on active block spaces the OS believes is either basic OS services and highly accessed elements from your active applications. As its a small drive that’s about all it will have on it. As its a cache drive everything on it is a copy! All of your stuff is on the HDD, the OS is only altering its pointers to which drive to pull the data (mostly OS or app). Here’s a useful deep dive if you want to know more How to make a custom CoreStorage drive in OS X its a bit dated! As Apple has altered things a bit with the newer macOS releases. But the foundations are the same. Anyways… Getting back to your issue, frankly the small SSD Apple uses it mostly useless if you split the Fusion Drive. I would leave it as a Fusion Drive unless you want to improve your systems performance! Then the issue is how deep do you want to dig in! To get the most I recommend replacing the small blade SSD with a much larger one, making it the boot drive holding your OS and apps. We also want a large enough drive so the OS level services of Virtual RAM, Caching (not FD here just normal caching) and app caching and scratch file space depending on your apps needs. Its a bit of work as you can see here iMac Intel 27" Retina 5K Display Blade SSD Replacement and the SSD does get expensive (480/512 GB or 1TB being the common choices) The other direction is removing your current HDD and switching it out with a SSD, this is a lot less work but you loose the higher data throughput of the PCIe/NVMe interface as the HDD interface is limited to SATA III (6.0 Gb/s) throughput iMac Intel 27" Retina 5K Display Hard Drive Replacement Here’s a deep dive into Apples drives and throughput The Ultimate Guide to Apple’s Proprietary SSDs
