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I'm about to buy a Mac Mini and have got the DIY Fusion Drive parts handy. I'm actually a bit on the fence about the choice of manual SSD+HDD separation with the aid of symlinks and proper Fusion Drive. Both have their pros and cons.

What worries me though are a couple of articles at Mac Performance Guide:

The author claims that he's not able to make the migration of frequently used data from the HDD back to the SSD to actually happen, placing blame on the fact that he's using a 3rd party SSD.

I haven't seen reports of this sort of problem anywhere else on the web. Has somebody here running a 3rd party SSD in a DIY Fusion Drive on a 2012 Mac Mini been able to actually verify that the data moves both ways, SSD -> HDD and HDD -> SSD? I mean real, hard proof backed by iostat or some other method proven to be valid.

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I would also be very interested to know. I did my own Fusion Drive and I am trying to see if it's working as it should, but until now, I can't see the real moving of data back to SSD. When I stop reading repetitively the same data, that is located on the HDD, it seems to continue to read/write. And then, I am reading from both drives. Like if half has been moved to the SSD. But even keeping reading and reading this same data, it never moves 100% to the SDD. – user46362 Mar 30 '13 at 17:10

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