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Question: Why system report and diskutil report 28GB instead of 32GB for the SSD part of my iMac 1TB Fusion drive?


I bought a 27" iMac Retina 5K (iMac18,3) with the 1TB Fusion drive. On the Apple store site it's written:

"The 1TB Fusion Drive pairs a 1TB hard drive with 32GB of fast SSD — enough to store important macOS files and applications to ensure fast start-up, near instant wake from sleep and quick application launching, with room left over for your most frequently used files and apps."

Source: Customise iMac - Apple (CA) (then click on the link "How much storage is right for you?")

If I check in System Report it clearly show 28 GB:

User uploaded file

And diskutil show the same thing:

User uploaded file

I also bring the iMac at the Genius Bar and asked them about this; they told that their diagnostic tools show an SSD of 32GB. They didn't want to check in diskutil or System Report. Strange...

For me 32GB it's already really small. If you reduce it by 12.5% to 28GB it doesn't help. This iMac is the family computer and we have four accounts running on it. We suffer regular slowdowns and beachballs.

But my main problem is that Apple didn't gives me what I bought, a Fusion drive with an SSD of 32 GB. It's false advertising, No?

What should I do?


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Apr 22, 2018 11:03 AM in response to etiennedeso In response to etiennedeso

After partitioning and formatting of any drive, there is a loss of storage space to the boot block, directory, and control software for the Fusion Drive. The SSD is not intended for your use. It contains the system software and a devoted buffer space that is used to help increase transfer rates to and from the main HDD.

You cannot use that SSD without breaking the Fusion Drive. Then you have a fairly useless SSD because it is too small for anything useful. In the Fusion Drive mode, the SSD becomes a larger than normal buffer to enhance the data transfer speed of the HDD.

Apple gave you exactly what you bought. It has an SSD with 32,000,000,000 bytes which inside the computer is about 29.8GBs of formatted space.

The only thing you should do is enjoy the computer because there is nothing wrong with it.

Apr 22, 2018 11:03 AM

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Apr 22, 2018 11:14 AM in response to Kappy In response to Kappy

If you check carefully the screenshots you can see that the SSD capacity is exactly 28,000,002,048 bytes and not 32,000,000,000 bytes. This is really the size of the SSD and not the remaining free space after the initialization. You can find the size after initialization just a few lines below and it's 27.55GB (or 27,551,166,464 bytes).

Apr 22, 2018 11:14 AM

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Question: Why system report and diskutil report 28GB instead of 32GB for the SSD part of my iMac 1TB Fusion drive?