Urgent Warning: Fusion Drive always consists of two separate disks. If you want your data back you must get both parts. We’ve heard a number of reports that users with failed Fusion Drives are only given the Hard Disk back when receiving Apple repairs. On its own, the hard drive is not enough to recover all data in original condition. This is especially true if FileVault encryption is used.
What is Fusion Drive?
Fusion Drive is Apple’s version of a hybrid solid state & mechanical disk. It combines a small fast SSD with a large slow hard drive to achieve a balance between cost & performance. Frequently used files are moved to the SSD, and old stale data is sent to the slow hard drive. This is all taken care of automatically behind the scenes. Unless you dig into the terminal, you wouldn’t even know you had two separate disks inside the Mac. Fusion Drive is part of Apple’s Core Storage system. It is somewhat similar to Linux LVM as a volume management system.
What Fusion Drive is not
Fusion Drive does not use the SSD as a cache for files but actually moves data from one disk to the other. This is important, as both disks are required for full recovery.
Why does Fusion Drive exist?
At launch, and even now, the cost for large capacity SSDs is way higher than the cost of an equivalent hard drive. The problem is that SSDs offer huge benefits to the user experience. When you use an SSD, you hardly ever have to wait for things to load. The computer boots up within seconds.
Hybrid drives aim to bridge the gap between solid state and mechanical disks. An iMac with a 3TB Fusion Drive comes with some of the benefits of SSDs, but much less cost. As the cost of SSDs fall, the need for Fusion Drive will eventually disappear. Apple has shown with their current lineup that they’d much rather go all-SSD where possible. Current iMac Pro & MacBook Pro both use 100% SSD internal storage.
We’ve had two recent cases where a user has brought a “Fusion Drive” to us for recovery, but actually only had the hard drive part. Apple had given the damaged hard drive back after replacement, but reused the SSD when creating a new Fusion Drive. This user only had a few GB of data so the Hard Drive hadn’t even been used yet. All the data was stored on the SSD which was now overwritten.
The majority of Fusion Drives we’ve seen have a Seagate ST3000DM001 3TB hard drive combined with a 128GB blade SSD.