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Can I replace the 1TB fusion drive in my 2017 base model iMac with a 10tb hdd, and a 512gb ssd? Will both drives fit in the iMac.

Yes! You can remove your current Fusion Drive set and replace one or both of the drives. As to your choices here, I think you’re pushing it, a 10 TB drive is just too big for your iMac (heat & power) It would also be less attractive trying to resell and its performance might not meet your needs limited to SATA III (6.0 Gb/s) throughput. For reference: Seagate Helium 10 TB HDDSeagate Barracuda 3~8 TB So what would I do?? I would limit the HDD to 4 TB as the largest SATA drive. Then you have the question of the PCIe/NVMe SSD drive. Frankly, I wouldn’t setup a Fusion Drive at all! I would configure the blade SSD as the boot drive with all of my apps and leave as much of the drive I can empty! So if I have 128 GB of Apps I would get a 512 GB SSD. This allows the system to leverage the rest of the SSD as virtual RAM as well as cache & paging space for the apps making them much faster! A bigger 1 TB would be even better for video editing! If speed is needed for the deeper storage I would go with a RAID’ed external Thunderbolt3 drive and not bother with the internal HDD at all! Last year I helped setup 4 iMac’s for video editing. Each was bought with 1 TB blade SSD’s and we configured OWC Express 4M2 external drives and lastly a very large NAS system for the video archive. OK, So how do you do this? First you’ll need to break the Fusion Drive set following this Split Your Fusion Drive Apart Then to take current HDD out you’ll need to follow this guide iMac Intel 27" Retina 5K Display Hard Drive Replacement and if you want to get to the blade SSD you’ll need to follow this guide iMac Intel 27" Retina 5K Display Blade SSD Replacement and here is the needed blade SSD Apple Proprietary PCIe 3.0 x4 interface SSD’s and here more info on the PCIe SSD’s The Ultimate Guide to Apple’s Proprietary SSDs which explains in great detail the different SSD’s Apple has used over the years.

Depend on the size of the drive. If your drive is too thick, it will not sit. The SSD used in the Mac is not the SATA3 2.5in but the PCIe drive with apple design. The display is glued to the body so you need to buy the adhesive strips to mount the display back. Update (03/02/2019)

That is 1TB drive and fusion drives have 128GB or 64GB depend on the model. The 3.5 are okay but too heavy and bulky so I usually use 2.5in 2TB drives for internal and the rest of data stored in external drive.

I’d like to remove the fusion drive all together because I think it is slowing the machine down. Will the 5k work without it?