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I have one of those in an ageing late 2009 27" iMac running Linux. It is a Seagate ST2000DX001-1CM1, a 2TB "SSHD" which comes down to having 8 GB of NAND storage bolted on to a conventional 2TB drive. It doesn't need any special driver to do its thing so I wonder what that CoreStorage bit is supposed to be about.

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Did you install that SSHD as an aftermarket upgrade? I thought the Fusion Drive configurations shipped by Apple used normal hard drives and separate SSDs and were purely software-managed (and also used much more than 8GB of flash).

No, this is the drive the machine came with from the factory.

You're probably wrong. The User Manual for Seagate ST2000DX001 has a revision history stating its first version was published in 2013. That drive was probably not being installed by Apple in the factory four years earlier. Apple didn't introduce "Fusion Drive" branding until 2012. The 2009 iMac models were discontinued in 2010. Nothing you're saying adds up.

Apple sold iMacs for many years that had a completely separate SSD and HDD, and CoreStorage was used to combine them into a single block device which was then partitioned and formatted as HFS+ or APFS.

You could also do this to your own SSD and HDD, though probably only a good idea with internal ones like in a Mac Pro

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