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I want to check the size of the SSD part of my Fusion Drive and if it makes sense to install a bigger SSD. I have a 3TB Fusion Drive and I suppose there is an 128GB SSD installed. Does it make sense to put in a 500 GB SSD as I have one left from upgrading my MacBook Air. And is there any diskutil procedure or repair mode action necessary to bind these drives together again or can I just flip the SSDs? Thank you very much.
Lets first look at why Apple intro’ed the Fusion Drive: At the time SSD’s where very expensive but wicked fast over slow HDD’s. People wanted both the deep storage of an HDD and the speed of an SSD. Both Seagate & Western Digital saw this and responded with two competing designs (hybrid drives - SSHD). Seagate offered a HDD with a SSD cache unit and WD offered a dual drive sandwiching a HDD & SSD into one device! Apple wanted to leverage their blade SSD development and copied the Seagate concept. But, unlike Seagate, Apple leveraged a faster PCIe interface its blade drives offered and handled the caching within the OS instead of within the drive unit. Fusion Drives where born! Lets jump forward back to today, the cost of nonproprietary 128 GB was pushing $200 back in 2011 today a 1 TB is less than $200! Sadly, proprietary SSD’s have not fallen as far as commodity drives. So today Fusion Drives are not needed for the same reasons and if someone does their research in buying a new system they would not buy it. Instead they would spend the money on getting a straight SSD system to gain the speed and get a large enough drive to support the applications and scratch space needed for the tasks the system was bought for. In your case the question then becomes a question of risks in opening the system to even get to the blade SSD and as Apple is using a proprietary SSD design. Then the higher cost of the proprietary drive Vs using an external RAIDed SSD Thunderbolt drive, or just replacing the SATA HDD to a SSD.
