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Difficult to find a 3TB SSD around plus they are expensive if you go to a 4TB and I do not know if 4TB can be supported by this model. But I can get a 2Tb and a 1TB 2.5” SSD and place them both in a 3.5 rack . That is, if possible, if the OS will recognize them and If I can plug in the adapter cables. Let me know if I am dreaming? or should I go 4TB SSD?
Your system does not have two 2 SATA drive bays it has one SATA bay (3.5”) and a PCIe blade connector on the logic board. As you are looking for two SSD’s you do need to think through the costs and risks of doing this internally and if the I/O channels will be offering the speed you are looking for. The SATA port is SATA III (6.0 Gb/s) the PCIe slot is a custom mSATA (6.0 Gb/s) AHCI interface. While you can get quite large 2.5” SATA SSD’s 4 TB being the largest, the largest Apple blade SSD if you can find it is 768 GB for this system. For both the I/O is limited by the SATA interface of 6.0 Gb/s. If you look at your external options you have Thunderbolt (10 Gbps) which you can get much better throughput! If you are into music creation or video editing I would strongly recommend getting an external RAID box with SSD’s as being a cheaper and less risky direction to host your work. I would leave the internal SSD drive as is (or install a 2.5” SSD) as your boot drive 512 GB should be enough to hold your OS and Apps. If you do video work you’ll likely want a 1 TB drive so you have more scratch space. I wouldn’t waste the effort (or money) on the blade drive.
Sure, you don’t even need a 1TB SSD, a 500GB would do. Then set it up with a large standard drive as a Fusion drive iMac Intel 27" EMC 2546 Blade SSD Replacement iMac Intel 27" EMC 2546 Hard Drive Replacement Here’s how to set up the fusion drive: https://www.lifewire.com/setting-up-fusi…
