Apple dumbed-down their 1TB fusion drive to a 24GB SSD. The 2TB fusion drive has a 128GB SSD. Here is a concrete example of the difference.
I recently set up both a mid-range and a high-end Oct 2015 imac. The former has the 1TB fusion drive and the latter has the 2TB fusion drive. During first start-up you can attach an external HDD time machine backup from which to transfer user files. I used the same external 1TB LaCie HDD containing about 150GB of files and connected by firewire 800 through the thunderbolt port on the imac.
Transfer time to the 1TB fusion drive was 2 to 3 hours, compared to less than half an hour for the 2TB fusion drive.
I recently set up both a mid-range and a high-end Oct 2015 imac. The former has the 1TB fusion drive and the latter has the 2TB fusion drive. During first start-up you can attach an external HDD time machine backup from which to transfer user files. I used the same external 1TB LaCie HDD containing about 150GB of files and connected by firewire 800 through the thunderbolt port on the imac.
Transfer time to the 1TB fusion drive was 2 to 3 hours, compared to less than half an hour for the 2TB fusion drive.
