How Fusion Drive Works
@thebigk
•
Oct 26, 2024
Oct 26, 2024
1.3K
Apple introduced the Fusion Drive in their latest line of Mac Mini and iMac. The fusion drive brings the best of the two worlds - mechanical hard disk drives and the latest solid state drives and presents it to the user as a single drive. Until now, Apple users had to choose between the two - regular HDDs and the SSDs, but now; thanks to the latest technology update that brings the capacity of the standard HDD storage and the faster read/write speeds of the solid state drives as a single package. I began searching on the Internet for how the new fusion drive works and found some really interesting information on various sources. Let me share it with you with simple and easy to understand words.
First of all, the Fusion Drive is basically a combo of two separate drives presented as one. That means, Fusion Drive is a summation of two parts acting as one. That is the reason the actual storage size of the Fusion Drives is 1.1 TB (128 GB of SSD + 1 TB of HDD). So what magic happens when you enable the Fusion Drive and store some data to it?
<a href="https://www.anandtech.com/show/6406/understanding-apples-fusion-drive" target="_blank" rel="noopener noreferrer">Understanding Apple's Fusion Drive</a> finds out that Apple creates a buffer of 4 GB on the NAND drive (SSD). All the writes that come to the drive are routed to this buffer first. The additional writes would be routed to the regular HDD. Having a 4GB cache ensures that the operations are faster for the user. Apple expects the 4GB buffer to be enough for the regular operations and that ensures performance for the HDD.
OSX Mountain Lion has been optimised to physically move the most frequently used files to the SSD, while other files are transferred to the HDD. The movement of files from SSD to HDD and vice versa is important to. Mountain Lion won't commit the moves unless the file transfers are complete. That means, in case of power failure, there won't be any data loss. The OS will simply make copy of the file in another location and once copy is successfully created, only then the original is deleted and space is freed up.
It's important to note that OSX still recognises the Fusion drives as two drives connected to the machine via SATA. A system report will mention two drives instead of just one. Interesting concept, isn't it?
First of all, the Fusion Drive is basically a combo of two separate drives presented as one. That means, Fusion Drive is a summation of two parts acting as one. That is the reason the actual storage size of the Fusion Drives is 1.1 TB (128 GB of SSD + 1 TB of HDD). So what magic happens when you enable the Fusion Drive and store some data to it?
<a href="https://www.anandtech.com/show/6406/understanding-apples-fusion-drive" target="_blank" rel="noopener noreferrer">Understanding Apple's Fusion Drive</a> finds out that Apple creates a buffer of 4 GB on the NAND drive (SSD). All the writes that come to the drive are routed to this buffer first. The additional writes would be routed to the regular HDD. Having a 4GB cache ensures that the operations are faster for the user. Apple expects the 4GB buffer to be enough for the regular operations and that ensures performance for the HDD.
OSX Mountain Lion has been optimised to physically move the most frequently used files to the SSD, while other files are transferred to the HDD. The movement of files from SSD to HDD and vice versa is important to. Mountain Lion won't commit the moves unless the file transfers are complete. That means, in case of power failure, there won't be any data loss. The OS will simply make copy of the file in another location and once copy is successfully created, only then the original is deleted and space is freed up.
It's important to note that OSX still recognises the Fusion drives as two drives connected to the machine via SATA. A system report will mention two drives instead of just one. Interesting concept, isn't it?
