Increase physical HD but not SSD on 2017 iMac Fusion Drive

You can however it's pretty unwise when most of your storage is likely media such as photos, music and movies. In that case, move those libraries to and external HD such as OWC Mecury Elite Pro, just buy 2 of them one for primary storage the second for backing up the primary. This is a much easier and less expensive proposition than attempting to upgrade the internal HD and rebuilding your Fusion drive.

It is possible. Just not very practical compared to moving a large library (music, photos, etc..) off to an External Drive.

To upgrade the Fusion Drive.

1. You would want to have good backups in place. (Time Machine and a Clone)
2. You would have to have or replace the HDD yourself without doing any damage.
3. You would have to refuse and format the existing SSD and the new 3T HDD.
4. You would need to install macOS and Restore from Time Machine or the Clone.

To move a large library off to an external drive.

1. You would need a good quality external drive to hold the library
2. You would need a good backup for both the internal and external drives.

2.5" plus you are going to need a display adhesive seal kit.

see >https://eshop.macsales.com/installvideos/imac-27-inch-5k-late-2015/

FWIW the last poor sole here got his iMac all back together and running, just to have the display fall out, break and pull the display connectors off the logic board.

k3comms wrote:

Do you know what physical size the HD is by any chance?

It uses a 3.5" hard drive.

You have to be very careful working on these newer iMacs because the displays are very fragile (especially the 27" one because it is so large & thin). The cables are also very hard to see and reach so it is very easy to damage the connectors on both the cables and the Logic Boards. The repair guides and videos may look like the iMac is easy to work on, but they can be deceiving.

you have some good advice here and a good plan, just want to add, that in the event someone did take on the challenge of opening up the machine to replace the original hard drive, it would be a better option to replace it with a faster SSD, as large as you can afford, and just split the Fusion drive and use the two internal SSDs individually, or as a JBOD RAID set. In any case, you would have to perform some Fission to split the Fusion drive when replacing the original. Also, they do make brackets so you can install a 2.5" SSD into a full size drive 3.5" bay, just an FYI.

Going to all the trouble to just increase storage space is not as good a reason as compared to if you want to increase the read/write performance/speed of the system. If you can boot and launch apps much faster on a new larger internal SSD, then you have a little bit more enticement to taking on that challenge. But for increased mass storage alone, speed is not such a big deal, and external drives are much simpler option to managing your data.

Keep a full backup of that internal Fusion drive, if one of the component drives fails, the whole system goes down. Have a bootable backup copy on an external drive, it will save your bacon later.

Doing surgery on 2012 and later iMacs is MAJOR surgery, pleaser review the video den.then provided and you will see. I still strongly recommend an external HD.

HWTech wrote:

It uses a 3.5" hard drive.

You are correct. The 2017 27" iMac, has a 3.5" hard drive.

My bad, somehow I got the 27" iMac mixed up with the 21.5" iMac which has a 2.5" drive.