Fusion Drive with internal and external SSD ?

[Antares23]

Hello everyone.

I have a Late 2013 27" iMac, with a 128GB PCIe SSD and 1TB HDD (Fusion Drive), but the HDD is clearly dying. (It will regularly disconnect while using it, disappearing from Disk Utility and System Information), so I stopped using it at all as its unreliable as hell.
The SSD is working fine tho.

But even if I try to offload as much as possible on that drive (which by the way is slow as hell, 30MB/s at best, so I only use it for storage, not for running Applications)
The 128GB SSD often fills up very quickly. Whether it's iCloud which keep downloading big files and folder to the SSD, even tho I don't need them, or the system data (in System Preferences/General/Storage) that can take a lot of space: a few days ago they took up to 60GB.

Considering I don't want to replace that HDD at the moment, because I'm not confident at all in trying to open these tappered edge iMacs, I've heard some horror stories about people breaking the glass trying to cut the adhesive, but also because I can't justify to spend 70€ for the iFixit upgrade kit+the price of the SSD.

So, as a temporary solution, I've thought about using a SSD+USB3.0 to Sata adapter, and create a Fusion Drive between the 128GB PCIe SSD and the USB 3.0 SSD. Would that work ? I don't think there's any reason why it wouldn't, as the OS and apps would probably be stored on the faster PCIe SSD, and the rest of my stuff would be stored on the external SSD, and it would definitely be less of a hassle than trying to organize everything with the drives split (Because, as an example: you can't move the iCloud Drive folder to another drive than your system drive, you can't move your Photos library if you want to use iCloud (which I do), and, as I've said, sometime system data or else tend to take a lot of space)

From what I've seen, I can expect about 400 to 500MB/s, which would be more than enough.
If the SSD is obviously always plugged into the Mac, when it starts ect, it shouldn't be treated any differently than a Fusion Drive with the internal HDD ?

(And.. No I can't use a Thunderbolt one, as they're expensive, and I have two display plugged into my Thunderbolt ports)

Thank you for those who will take the time to read this and give me some answers !

 

[sack_peak]

Fusion drive is only with the SSD + internal drive. Cannot be with external drive regardless whether USB or TB.

You could have a internal PCIe SSD + internal SATA SSD.

Did you buy this iMac brand new during its 1st year of release?

 

[Antares23]

Fusion drive is only with the SSD + internal drive. Cannot be with external drive regardless whether USB or TB.

You could have a internal PCIe SSD + internal SATA SSD.

Did you buy this iMac brand new during its 1st year of release?

So, If I tried to create a Fusion Drive using

diskutil apfs createContainer -main disk0s2 -secondary disk1s2

for example, It wouldn't work for the sole reason that it's a USB drive ?
I've already split, and rebuilt the Fusion Drive with that command and it worked. (but only with both internal drive tho, might have to try with external one to see)

Yeah, that would be the ideal solution obviously, but as I've stated, I won't open this iMac for the moment.

It was bought in May 2014. But I'm not the first owner, I've bought this iMac in late august this year. For the price I've paid for it (280€) it was a really good deal. (Considering I've literally saw every single ad for iMacs on Leboncoin (French Craigslist basically), this was a steal, even with the dying HDD)

 

[sack_peak]

So, If I tried to create a Fusion Drive using

diskutil ap createContainer -main disk0s2 -secondary disk1s2

for example, It wouldn't work for the sole reason that it's a USB drive ?
I've already split, and rebuilt the Fusion Drive with that command and it worked. (but only with both internal drive tho, might have to try with external one to see)

I skimmed through your detailed post. If it works internal + external then great for you.

 

[Antares23]

So, I've just tried with the internal HDD and a random USB thumb drive I had lying around (the USB drive marked a external when I list the drives with diskutil list) and it worked, it created a Fusion Drive with the Internal HDD and the USB drive.
Didn't tried to install macOS on it, but it seems promising.

 

[Fishrrman]

I'd avise against trying this.

Yes, it's technically possible, but still NOT a good idea.
One inadvertent disconnection could trash the fusion drive.

Yes, you do need an external SSD (I'd recommend a Samsung t7 "shield" -- fast and cheap).

But... don't fuse it with the internal 128gb SSD.
Just let them both exist as "independent" SSDs -- one internal, the second external.

You could set up the internal SSD to be a "small" boot drive.
Don't keep much on it. Just the OS, apps, and "slimmed-down" account.

Or... set up the SSD as the new boot drive. A USB3 drive will give you read speeds around 420MBps or so.

What kind of speeds are you getting from the fusion drive RIGHT NOW?

 

[sack_peak]

I'd avise against trying this.

Yes, it's technically possible, but still NOT a good idea.
One inadvertent disconnection could trash the fusion drive.

Yes, you do need an external SSD (I'd recommend a Samsung t7 "shield" -- fast and cheap).

But... don't fuse it with the internal 128gb SSD.
Just let them both exist as "independent" SSDs -- one internal, the second external.

You could set up the internal SSD to be a "small" boot drive.
Don't keep much on it. Just the OS, apps, and "slimmed-down" account.

Or... set up the SSD as the new boot drive. A USB3 drive will give you read speeds around 420MBps or so.

What kind of speeds are you getting from the fusion drive RIGHT NOW?

I would do this and heed his warning.

 

[lostless]

Yeah. Don’t fuse with the external. Just use a USB ssd as your main boot drive. The Mac will boot and run off the external Just fine. USB3 being your only speed barrier.
Just did something similar to my Mom’s 2017 iMac with a Dying hard drive. But have advantage of thunderbolt getting 800 MB up-and-down approximately

 

[Antares23]

I'd avise against trying this.

Yes, it's technically possible, but still NOT a good idea.
One inadvertent disconnection could trash the fusion drive.

Yes, you do need an external SSD (I'd recommend a Samsung t7 "shield" -- fast and cheap).

But... don't fuse it with the internal 128gb SSD.
Just let them both exist as "independent" SSDs -- one internal, the second external.

You could set up the internal SSD to be a "small" boot drive.
Don't keep much on it. Just the OS, apps, and "slimmed-down" account.

Or... set up the SSD as the new boot drive. A USB3 drive will give you read speeds around 420MBps or so.

What kind of speeds are you getting from the fusion drive RIGHT NOW?

I don't have Fusion Drive right now, because of the dying HDD, I became too impatient waiting for the OS to install, so I split the Fusion and only installed macOS on the 128GB SSD, and also because that HDD is unreliable and will disconnect randomly (so, basically the same problem as what could happen with a USB Fusion Drive)
But I'm getting 250MB/s write, 700MB/s read on the PCIe SSD.
Yeah, I think. I might do that.
I guess I could manage keeping the OS and apps on the internal SSD, and document+bigger apps/games on the external one.
There's still the hassle of iCloud Drive but I think I can manage it.

Yeah. Don’t fuse with the external. Just use a USB ssd as your main boot drive. The Mac will boot and run off the external Just fine. USB3 being your only speed barrier.
Just did something similar to my Mom’s 2017 iMac with a Dying hard drive. But have advantage of thunderbolt getting 800 MB up-and-down approximately

Yeah, I'd like to get a Thunderbolt one as it would be the ideal solution, but for the price of a Thunderbolt 2 enclosure (I think it's TB2 on the 2013)+SSD, we're getting very close to the price of the iFixit upgrade kit to actually install it inside.

 

[Antares23]

So, I've found another solution, I've found out that you can move your Home folder to another drive, so I did, I moved my home folder to the 2TB external HDD and it now works perfectly, the OS and apps are on the SSD and my home folder (and therefore iCloud Drive) are located on the external HDD.
I know that, like if I did a Fusion Drive, I shouldn't ever unplug the drive while the OS is running, but I've set it up in a way that it wouldn't.

 

[Brian33]

Do you only have 1 account set up?

You might want to set up an "emergency use" admin account with its home directory remaining on the internal ssd. If your only account's home directory is on an external and it dies, I think the machine wouldn't boot anymore. (Not sure about booting recovery, though.)

 

[Antares23]

Do you only have 1 account set up?

You might want to set up an "emergency use" admin account with its home directory remaining on the internal ssd. If your only account's home directory is on an external and it dies, I think the machine wouldn't boot anymore. (Not sure about booting recovery, though.

Yes I only have one account set up.
It could be a good idea, I also have everything backup up on another HDD + iCloud Drive
So I wouldn’t loose anything
Just the time needed to reinstall macOS but I have a SD Card with Ventura and OCLP on it, so even if the system crash I can reinstall it

 

[ignatius345]

I know that, like if I did a Fusion Drive, I shouldn't ever unplug the drive while the OS is running, but I've set it up in a way that it wouldn't.

That doesn't mean it will never disconnect, unfortunately. Whatever you do, make sure you're running good backups because it is not at all unheard of for an external drive to unmount itself.

 

[Antares23]

That doesn't mean it will never disconnect, unfortunately. Whatever you do, make sure you're running good backups because it is not at all unheard of for an external drive to unmount itself.

Yep. So, turns out that performance really isn't all that great (I didn't thought that the speed of /home drive would matter but looks like it does)
I'll bring the iMac to a repair shop next month to replace the dead HDD by a 1TB Samsung SSD. Then I might do a Fusion Drive again between the two SSD, the performance should be great I think.
The repair shop charges 110€ for the installation of the SSD, but that doesn't include the price of the SSD, so that would be 170€. A bit pricy to be honest but I can justify it, I'd rather not try to do it myself and break the glass.

 

[ignatius345]

Yep. So, turns out that performance really isn't all that great (I didn't thought that the speed of /home drive would matter but looks like it does)
I'll bring the iMac to a repair shop next month to replace the dead HDD by a 1TB Samsung SSD. Then I might do a Fusion Drive again between the two SSD, the performance should be great I think.
The repair shop charges 110€ for the installation of the SSD, but that doesn't include the price of the SSD, so that would be 170€. A bit pricy to be honest but I can justify it, I'd rather not try to do it myself and break the glass.

That's actually not a terrible price for the labor. I don't know about that 2013 iMac, but I opened up my 2014 iMac 5K to replace a dying Fusion Drive a few years ago. I spent I think around $80 on the repair kit (tools, parts, new adhesive strips) and then spent a couple hours on the procedure. 110€ doesn't sound bad to spare yourself the work.

Before you think about using that 128GB blade SSD in there, do yourself a favor and download DriveDx (the demo version will work) and see what the wear level is. On my iMac, it was very worn down and I just put in a new internal SATA SSD and made that the boot drive. It was plenty fast enough. I just don't know how much of a real advantage you'd get out of making a Fusion Drive if the big SATA drive is already an SSD.

 

[17fox]

Hello everyone.

I have a Late 2013 27" iMac, with a 128GB PCIe SSD and 1TB HDD (Fusion Drive), but the HDD is clearly dying. (It will regularly disconnect while using it, disappearing from Disk Utility and System Information), so I stopped using it at all as its unreliable as hell.
The SSD is working fine tho.

But even if I try to offload as much as possible on that drive (which by the way is slow as hell, 30MB/s at best, so I only use it for storage, not for running Applications)
The 128GB SSD often fills up very quickly. Whether it's iCloud which keep downloading big files and folder to the SSD, even tho I don't need them, or the system data (in System Preferences/General/Storage) that can take a lot of space: a few days ago they took up to 60GB.

Considering I don't want to replace that HDD at the moment, because I'm not confident at all in trying to open these tappered edge iMacs, I've heard some horror stories about people breaking the glass trying to cut the adhesive, but also because I can't justify to spend 70€ for the iFixit upgrade kit+the price of the SSD.

So, as a temporary solution, I've thought about using a SSD+USB3.0 to Sata adapter, and create a Fusion Drive between the 128GB PCIe SSD and the USB 3.0 SSD. Would that work ? I don't think there's any reason why it wouldn't, as the OS and apps would probably be stored on the faster PCIe SSD, and the rest of my stuff would be stored on the external SSD, and it would definitely be less of a hassle than trying to organize everything with the drives split (Because, as an example: you can't move the iCloud Drive folder to another drive than your system drive, you can't move your Photos library if you want to use iCloud (which I do), and, as I've said, sometime system data or else tend to take a lot of space)

From what I've seen, I can expect about 400 to 500MB/s, which would be more than enough.
If the SSD is obviously always plugged into the Mac, when it starts ect, it shouldn't be treated any differently than a Fusion Drive with the internal HDD ?

(And.. No I can't use a Thunderbolt one, as they're expensive, and I have two display plugged into my Thunderbolt ports)

Thank you for those who will take the time to read this and give me some answers !

Thanks for the interesting question! First of all, I'm not entirely sure if you can create a Fusion Drive between your internal and external SSDs, that's not how it works. A Fusion Drive is typically a combination of an HDD and an SSD, which is why I believe it neither makes sense nor is possible. However, you can always try and share your results, I could actually be wrong.
When it comes to booting up from an external SSD, it's no different from booting from your internal drive. Just set it up as the startup disk, and that's it. By the way, have you tried fixing your Fusion Drive with 'diskutil ResetFusion' command prompt and then reinstalling the system? This command helped me fix a split Fusion Drive and dramatically improved my reading and writing speeds. I now achieve around 800 MB/s for writing and 1200 MB/s for reading, respectively. These speeds are similar to what I had with my external SSD, which I am not currently using, but at the same time it's rather for testing purposes and if speeds actually decrease, I will switch back to my external SSD.