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1TB Fusion / 24GB SSD

Weaselboy

Weaselboy

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Jan 23, 2005
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Larry L said:
Hello, go to about this Mac and scroll down to NVMe and you will see it. As far as El Capitan being loaded on the SSD, I confirmed this with Apple as well
Click to expand...
Interesting, so in System Report you are seeing a 32GB flash drive? Can you run the command below in Terminal and paste up the output? That will show us the drive layout.

Code: 
diskutil cs list

Whoever told you the OS is on the flash drive is mistaken. A Fusion drive is one large virtual drive managed at the block level by the OS, and parts of the OS can be on either the flash or hard drive portion of the virtual drive depending on usage. There is just no direct way to tell where it is.
 
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Fishrrman

Fishrrman

macrumors Penryn
Feb 20, 2009
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Weaselboy wrote above:
"Interesting, so in System Report you are seeing a 32GB flash drive?"

I believe the PCIe flash drive in the "1tb fusion" iMac is in reality a 32gb drive, with approximately 8gb of that space "provisioned off", to be utilized incrementally in the future as the "live" memory cells wear out.

Apple can't be paying all that much for these blade drives.
They should have at least used a 64gb flash drive (perhaps with 8gb provisioned for a usable space of 55-56gb) in the low-end fusion model...
 
Weaselboy

Weaselboy

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Fishrrman said:
I believe the PCIe flash drive in the "1tb fusion" iMac is in reality a 32gb drive, with approximately 8gb of that space "provisioned off", to be utilized incrementally in the future as the "live" memory cells wear out.
Click to expand...

If that were the case it would show 24GB capacity in system report. Over provisioned space is not seen by the OS.
 
M

MadDane

macrumors 6502a
Apr 5, 2015
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Looking at the teardown of the late 2015 27" iMac, it does say 32GB on the card.

iMac27inch-5k-late2015-102.jpg


Link: http://blog.macsales.com/33572-owc-unboxes-tears-down-the-late-2015-27-inch-imac-retina-5k
 
Weaselboy

Weaselboy

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maflynn

maflynn

macrumors Haswell
May 3, 2009
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Weaselboy said:
Over provisioned drives I have seen always only show the usable space
Click to expand...
Perhaps Apple is using a proprietary method and it won't show as provisioned.

Tbh, I think it makes a lot of sense that apple is using 32GB because 24GB is an odd size.
 
M

MadDane

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Apr 5, 2015
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Weaselboy said:
Interesting find... but I still don't think it shows 32GB in System Report or diskutil. Over provisioned drives I have seen always only show the usable space. I'd like to see a System Report screenshot of someone with one of these.
Click to expand...
As far as I know it only shows 24GB in the system report. But yes, it would be interesting to see from someone who has that model. Otherwise I'll have to check next time I am at a store that has one :)
 
Fishrrman

Fishrrman

macrumors Penryn
Feb 20, 2009
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It's 32gb. Actually, this fact was revealed some time ago.

I reckon that the "2tb fusion" iMac (perhaps the Mac Mini models, too) uses a 128gb SSD module, with 8gb "secretly provisioned off" and the remaining 120gb or so available for CORE storage.

The idea is to fend off "SSD drive failures" due to too many used-up memory cells. By having an overly-large reserve of provisioned cells, Apple is hoping that they don't have to replace many of these in the future...
 
Hellhammer

Hellhammer

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Dec 10, 2008
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The capacity "loss" is likely explained by Fusion Drive's write cache, which is 4GB. The cache may be in SLC mode (which would explain why 8GB is lost), or there could be some additional over-provisioning.
 
AndreeOnline

AndreeOnline

macrumors 6502a
Aug 15, 2014
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Digging up this old thread:

I've got this exact drive. Capacity is reported as 24GB.

Did anyone replace this with higher capacity? Do I need to look for an actual Apple part, or will any of the newer 3rd party drives do? I seem to find contradicting (and perhaps a bit old) info when googling.

EDIT: and interestingly, the system reports 'removable: No'. It does look very removable in the photo above.
 
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cynics

macrumors G4
Jan 8, 2012
11,959
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Weaselboy said:
Whoever told you the OS is on the flash drive is mistaken. A Fusion drive is one large virtual drive managed at the block level by the OS, and parts of the OS can be on either the flash or hard drive portion of the virtual drive depending on usage. There is just no direct way to tell where it is.
Click to expand...

+1

I bolded that part because its critical to understand its operating at a block level. That means not only can a portion of a program be on the SSD and the other on the HDD but a portion of a individual file can be spread out across both.

Because of that its unlikely the entire OS is the on the SSD portion. If you don't use Garage Band or iMovie or even specific core functions of the OS there is little reason for them to reside on the SSD.
 
AndreeOnline

AndreeOnline

macrumors 6502a
Aug 15, 2014
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cynics said:
I bolded that part because its critical to understand its operating at a block level.
Click to expand...

And I've been quietly wondering if that is the underlying cause to why I'm seeing intermittent 'write to disk errors' in Catalina.

My iMac is from 2015 and I guess this little 24GB SSD is getting worn.

That said, I'm leaning more towards it being a Catalina issue.
 
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