Multiple hard drives on my iMac causing problems

[aboswell]

I bought a secondhand Imac this year. It wa being used by a graphic design company that is now out of business. It has been running well so far, but now the storage is “maxed out” and I cannot even download iOS updates. The “system” memory is completely full (I have noticed this is a software issue for some people).

But what I have discovered is that there are 2 hard drives. One small one that appears to be running the iOS and another large one that just seems to be used for storage.

However, everything is being downloaded/updated to the small drive and it is maxed out and I assume a full hard drive will also affect the speed/performance of the MAC. Why would they lay it out like this??

I’m planning on reinstalling Mohave now. I have it on a bootable USB drive. Can someone give recommendations on how to layout/format/install across 2 hard drives to optimise the performance of this MAC. I’d assume using the bigger drive with more storage would allow for less problems and faster hard drive speed. Am I missing soemthing? Appreciate rhe help!

 

[iRaynor SK]

2 hard drives? Looks like you have iMac with Fusion Drive.

 

[Fishrrman]

OP:

Do you have Mojave installed now?
If not, what OS is installed?

IMPORTANT QUESTION:
When you boot up, and get to the finder, do you see ONE hard drive icon, or do you see TWO of them?

If you see TWO, you -might- have an iMac that originally had a "fusion drive", but the two internal drives that were "fused together" are now UN-fused.

We need to know that before going further.

 

[getrealbro]

The one hard drive in the iMac may be partitioned into a System and Data partition. That's how ALL of our Macs have been setup since before OS X. Use Disk Utility to see all the mounted drives and partitions.

GetRealBro