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TOPIC: Can an eDrive be built on a fusion drive?

Can an eDrive be built on a fusion drive? 09 Nov 2017 12:28 #8800

As the question asks, really. I'm about to get a computer with both HDD and SDD drives which I will be making into a fusion drive, then installing Mavericks clean and migrating all my data via Time Machine.

Having done all that, will I be able to build a TTP9 eDrive on the fusion drive? I only ask because Apple's own Recovery Partition isn't put onto a fusion drive as part of the install, so I need to know if an eDrive can be.
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Can an eDrive be built on a fusion drive? 09 Nov 2017 14:05 #8801

The answer to this question used to be no, that the volume that appears as the Fusion Drive could not be split to create an eDrive. This document claims that all tests and tools can be used, except for the disk optimizer:

Fusion Drive Compatibility

I urge you to make a backup of all of the contents of the Fusion Drive before attempting to make an eDrive. If you have another drive, that might be a better place to put the eDrive, in case there is a problem with the Fusion Drive's hardware.
MicroMat Inc
Makers of TechTool
Last Edit: 09 Nov 2017 14:06 by micromattech3.
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Can an eDrive be built on a fusion drive? 09 Nov 2017 14:41 #8803

Thanks for the quick response. I could avoid this uncertainty by creating a separate small partition for the eDrive (it needs 20GB, right?) on the HDD and building the eDrive when all else is done.

Would that work though, as the eDrive is 'invisible' (like a standard Recovery Partition), so can it exist in its own personal visible separate partition?
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Can an eDrive be built on a fusion drive? 09 Nov 2017 14:54 #8804

You are welcome.

The eDrive cannot be created on a volume that you created yourself. It is created by using the eDrive pane in the Tools part of the TechTool Pro application. You chose a volume to be the eDrive destination volume, and that volume gets split to create the eDrive. There is a screen capture in the TechTool Pro 9 manual, available in the Help menu of the application.
MicroMat Inc
Makers of TechTool
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Can an eDrive be built on a fusion drive? 09 Nov 2017 15:32 #8805

Sorry, I wasn't too clear in my second post. The situation is this:

The computer has a 1TB HD and 128GB SSD. I plan to make a 50GB partition on the HD for Sierra, which I don't intend to use (much) at this stage. The remainder of the HD + SSD would be used for the fusion drive.

However, if there was any doubt about whether the eDrive could be created on the fusion drive, what if I created another 20GB partition on the HD BEFORE creating the fusion, installing Mavericks, and migrating my stuff? Then AFTER I'd done all that, I could launch TTP9, use the fusion drive as the source volume, and the 20GB partition on the HD as the destination - would that work? (Effectively, according to your manual's screenshot, the HD partition created for the eDrive would be 'external' as it wouldn't be part of the fusion drive).
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Can an eDrive be built on a fusion drive? 09 Nov 2017 15:40 #8806

The approach you have suggested will not work, because the eDrive is created by splitting an existing volume. If you create some volume, and then choose it as the eDrive Destination Volume, the volume you created is going to be split, not simply copied to. The system software tools cannot split a volume smaller than 32 GB, so you will have to make a volume at least that large, and whatever is left over after it is split to create the eDrive is going to be wasted space.
MicroMat Inc
Makers of TechTool
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Can an eDrive be built on a fusion drive? 09 Nov 2017 16:12 #8807

So sorry to drag this out! But I do need to be sure, as I've never created an eDrive or used a fusion drive before.

This should work then: if I make the Sierra partition big enough to split between use for Sierra AND an eDrive - 70-80 GB say - then this would be used by TTP9 to split 20GB off for the eDrive, leaving me the remainder to use to install Sierra on later?
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Can an eDrive be built on a fusion drive? 09 Nov 2017 16:28 #8808

That approach should work.

I suggest you create the eDrive first, as you have specified, in case something goes wrong. Creating an eDrive involves writing to the partition map of the device, which is a task Apple has always suggested be preceded by a backup.
MicroMat Inc
Makers of TechTool
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Can an eDrive be built on a fusion drive? 09 Nov 2017 18:30 #8809

Ok! And I can create the eDrive from my present computer (running Mavericks) to the blank partition on the other computer, which will be connected in Target Disk Mode?
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Can an eDrive be built on a fusion drive? 09 Nov 2017 19:21 #8810

I am not sure whether the eDrive can be created in Target Disk Mode. You will have to try that. I have suggested it in the past, but people have not reported whether it worked or not.

The problem is that an eDrive created using system software from one computer may not boot another computer running a different version of the system software, or even the same version, because the system software installed on one computer may not support the video hardware of another. You will have to try that, as well.
MicroMat Inc
Makers of TechTool
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Can an eDrive be built on a fusion drive? 09 Nov 2017 19:26 #8811

That's why I wouldn't create the eDrive first, but AFTER all the other setup and migration has been done. However, I shall certainly create the partition for it and Sierra first, as we discussed above. Thanks.
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Can an eDrive be built on a fusion drive? 09 Nov 2017 20:22 #8812

You are welcome.
MicroMat Inc
Makers of TechTool
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