How do dual SSDs work?

[iamsen47]

I'm not a hardware guy so this is probably a silly question. I'm intending on replacing the DIY fusion drive in my mini with dual SSDs. A long time ago, in an OS far, far away, I vaguely remember something about C drives and D drives. How does mac handle multi drives?

Would it still be treated as a single volume like the fusion drive or would the second drive appear as a separate device in finder like a usb drive?

Would I have to manually 'move' things over or would the OS automagically sort things for me?

 

[Weaselboy]

When you remove one of the existing drives, you are going to "break" the Fusion drive and the OS and all your data will be gone. What you want to do before you do that is backup everything to an external drive using Time Machine.

Then when you install the new drive, you will need to boot to the Time Machine backup and restore everything to one of the SSDs. Or you could manually make the two SSDs back into one Fusion drive if you like.

 

[iamsen47]

I'm actually planning on doing a fresh install of Sierra since the mini was also my first mac and as a learning machine I've installed way too many things that I don't remember about anymore. I'm planning a more developer centric setup that I'll later propagate to my other macs. Both SSDs are brand new.

Thing is, my other machines are all laptops so I don't have any experience with a Mac with 2 separate volumes so I want to know how the second volume works. Is it treated as something totally separate like a USB memory where I'll have to 'manually' move things in, or if OS X will still sort things out automagically?

If it's a separate volume and let's say I use it purely for storing docker images and jar files, how would I target this particular volume?

Or maybe if there's also a way for OS X to link both drives together into a single volume, like a JBOD?

 

[Yahooligan]

Yes, if you connect 2 drives without doing anything like RAID0 or Fusion then you will basically have a primary boot drive and then a secondary drive that doesn't do anything until you move things to or install things on it. macOS will not utilize both drives automatically by default. If you want to use the second SSD as a data drive then that's fine, you would access it just like you access the primary drive only you'd give it a different name. For example, one drive could be "Macintosh HD" and the other could be "Data" or whatever you want to name it.

 

[Weaselboy]

Or maybe if there's also a way for OS X to link both drives together into a single volume, like a JBOD?

You could manually configure it as a Fusion drive, then it would appear as one volume. But otherwise it will appear very much like the USB drive you mentioned and you will have to manually move things to the drive.