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Fusion vs Alternatives
Update, July 2017: MPG no longer recommends the Fusion option because SSD (flash drive) pricing is reasonable, with far higher performance. MPG advises at lesat 512GB internal flash drive, preferably 1TB or 2TB, coupled with high capacity external Thunderbolt storage.
Based on performance observed with medium-sized Photoshop tests, MPG recommends the Fusion option for the iMac. The internal Apple 768GB SSD option is also a fine choice, but very expensive with modest capacity.
Alternative pure SSD solutions can be faster and with guaranteed performance, but this general recommendation for Fusion rests on several realities:
- The Fusion option works well for small and medium sized tasks which demand less than 4GB of write buffering at any one burst.
- The innards of the iMac are difficult to upgrade (really feasible only by skilled personnel), therefore the Fusion option is best chosen and left alone as-is.
- Adding drives to the iMac adds cable mess so a reasonably fast Fusion drive cuts down the drive mess by one drive.
This all sounds good, but some users might take pause: Adobe Photoshop Lightroom users are better served by dedicating a large SSD to the catalog(s) folder(s) so that all operations on the catalog and viewing the previews is guaranteed fast. A Fusion drive cannot meet this need.
1TB or 3TB Fusion?
The question is whether to get the 1TB or the 3TB Fusion option. Here the 3TB option is recommended simply because of the difficulty of upgrading, and the fact that larger hard drives stay faster as they are filled up. However, anyone anticipating total storage needs of 600GB or less might as well stick with the 1TB Fusion option.
Fusion is a relatively expensive upgrade. Another option is to boot off an external USB3 SSD, such as the OWC Mercury Elite Pro Mini or the Newer Technology Mini Stack 960GB SSD and/or to use more than one USB3 SSD as convenient fast storage.
Guaranteed maximum speed
User needing additional ultra-fast drive performance should consider the OWC Mercury Accelsior in Mercury Helios enclosure solution (via Thunderbolt). Its speed is at least 50-100% faster than the SSD portion of the Fusion drive, and this speed does not vary as capacity is used.
Another alternative is to pony up for the Apple 768GB SSD. As a pure SSD, its performance should remain high up to near full capacity. This is the best solution for maximum internal performance (at least until OWC comes up with an internal upgrade, such as the Viper 6G SSD). And it does not preclude also adding the external OWC Accelsior+Helios SSD solution, discussed in the next paragraph.