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Baking a ssd + ssd Fusion drive in 2025

T

toke lahti

macrumors 68040
Original poster
I'm finally back on this.
Got hw for this over an year go.

Goal: making a Fusion drive.

Parts are:
  1. Part of very small INTERNAL drive of mini2018.
  2. TB connected big ssd.
First: volumes that are Fusioned has to be hfs+.
Host OS for fusioning: macOS Sonoma 14.8.2.

1st try:
Code: 
mini-me@mini-fusion ~ % diskutil apfs createContainer disk0s2 disk1s2
Creating container with disk0s2 disk1s2
Started APFS operation on disk1s2 (slowFusion)
Creating a new empty APFS Container
Unmounting Volumes
Switching disk1s2 to APFS
Switching disk0s2 to APFS
Creating APFS Container
newfs_apfs: unable to format /dev/disk1s2: Invalid argument
It looks like you are trying to create an upside down Fusion: Main tier (1862 GB) is larger than Tier2 (186 GB)
Error: -69626: Unable to create a new APFS Container
WOW!
Diskutil has evolved to be quite interactive!

Then, after a failure, you need format (erase) those hfs+ partitions again.

2nd try:
Code: 
mini-me@mini-fusion ~ % diskutil apfs createContainer disk1s2 disk0s2
Creating container with disk1s2 disk0s2
Started APFS operation on disk0s2 (hfs+INT)
Creating a new empty APFS Container
Unmounting Volumes
Switching disk0s2 to APFS
Switching disk1s2 to APFS
Creating APFS Container
FusionLC autodetect: regular Fusion
Created new APFS Container disk4
Disk from APFS operation: disk4
Finished APFS operation on disk0s2 (hfs+INT)

Now @diskutil:
Code: 
/dev/disk4 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +2.2 TB     disk4
                                 Physical Stores disk1s2, disk0s2

...to be continued...
 
I maybe being stupid here. But from your description your SSD is the largest disk.

The purpose of a fusion drive is using a small SSD for the operating system and then a larger standard hard drive for everything else.

If that’s what you’re doing I’m not sure making a Fusion Drive makes sense.
 
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hg.wells said:
I maybe being stupid here. But from your description your SSD is the largest disk.

The purpose of a fusion drive is using a small SSD for the operating system and then a larger standard hard drive for everything else.

If that’s what you’re doing I’m not sure making a Fusion Drive makes sense.
Click to expand...
My mini has small internal and very fast ssd. I also have a lot bigger, but not so fast 2TB ssd.
I fusioned them together.
I get the combined space, where I can fit all my home directory data and use the system practically with the speed of internal ssd.

Idea of Fusion is to merge fast and small to slower and big.

Have you ever bought an ssd and have calculated how much speed and space you get for a dollar?
 
Code: 
mini-me@mini-fusion ~ % diskutil apfs addVolume disk4 apfs intExtFusion
Will export new APFS Volume "intExtFusion" from APFS Container Reference disk4
Started APFS operation on disk4
Preparing to add APFS Volume to APFS Container disk4
Creating APFS Volume
Created new APFS Volume disk4s1
Mounting APFS Volume
Setting volume permissions
Disk from APFS operation: disk4s1
Finished APFS operation on disk4
Code: 
+-- Container disk4 3B937EDF-A9B2-43FB-8E6C-01F0370C184B
    ====================================================
    APFS Container Reference:     disk4 (Fusion)
    Size (Capacity Ceiling):      2200324751360 B (2.2 TB)
    Capacity In Use By Volumes:   8917626880 B (8.9 GB) (0.4% used)
    Capacity Not Allocated:       2191407124480 B (2.2 TB) (99.6% free)
    |
    +-< Physical Store disk1s2 9A57EB13-A9E8-49BF-90B5-46339CAF82C8
    |   -----------------------------------------------------------
    |   APFS Physical Store Disk:   disk1s2 (Secondary, Designated Aux Use)
    |   Size:                       2000189177856 B (2.0 TB)
    |
    +-< Physical Store disk0s2 6077DD79-315F-4C6A-95E8-C68170C4FCBE
    |   -----------------------------------------------------------
    |   APFS Physical Store Disk:   disk0s2 (Main, "Faster" Disk Use)
    |   Size:                       200135573504 B (200.1 GB)
    |
    +-> Volume disk4s1 11E464AB-B463-46A3-B5FD-30C468B829D6
        ---------------------------------------------------
        APFS Volume Disk (Role):   disk4s1 (No specific role)
        Name:                      intExtFusion (Case-insensitive)
        Mount Point:               /Volumes/intExtFusion
        Capacity Consumed:         815104 B (815.1 KB)
        Sealed:                    No
        FileVault:                 No
 
toke lahti said:
My mini has small internal and very fast ssd. I also have a lot bigger, but not so fast 2TB ssd.
I fusioned them together.
I get the combined space, where I can fit all my home directory data and use the system practically with the speed of internal ssd.

Idea of Fusion is to merge fast and small to slower and big.
Click to expand...

I assume you are trying to make an external USB SSD “faster”. If Fusion Drive external component a USB external SSD, would be interested in some read/write performance metrics.

Thinking you might be better served switching a brittle Frankenstein Fusion Drive set up to a dedicated Thunderbolt 3 external enclosure? Either way, different strokes for different folks. Carry on.
 
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You're doubling your risk of data loss with this setup, if either one of those devices fails, you lose everything. Having an external device in the mix makes it even more risky – what happens if the device is accidentally disconnected?

You could get the benefit of both devices with less risk by moving your home folder to a volume on the external storage.
 
And this is what you get with this ssd + ssd Fusion.
Looks pretty okay to me.
Faster drive first takes the heat and then transfers it to slower drive.
Although I'd need to have faster external source, bur right now I don't have the time put my mbp to target mode and copy something over TB3...

1. Copying a file from outside of the Fusion, but from partition of the internal ssd.
Code: 
mini-me@mini-fusion ~ % iostat -d disk1 disk0 1
              disk1               disk0
    KB/t  tps  MB/s     KB/t  tps  MB/s
    0.00    0  0.00     4.00    1  0.00
    4.00    7  0.03    12.76  157  1.96
   35.00    4  0.14   154.38 1683 253.74
  128.00    8  1.00   231.52 8490 1919.57
    0.00    0  0.00   228.04 7018 1562.89
    0.00    0  0.00   226.84 7049 1561.54
  128.00    2  0.25   225.77 7029 1549.66
    0.00    0  0.00   226.43 6985 1544.64
  128.00    1  0.12   226.99 6984 1548.21
  128.00    1  0.12   226.24 7124 1573.89
  128.00    1  0.12   225.11 7103 1561.48
    0.00    0  0.00   225.87 7067 1558.81
    0.00    0  0.00   227.22 7077 1570.31
  128.00    2  0.25   226.18 7002 1546.63
  128.00    3  0.37   227.56 7120 1582.24
    0.00    0  0.00   227.10 7052 1563.92
              disk1               disk0
    KB/t  tps  MB/s     KB/t  tps  MB/s
    0.00    0  0.00   225.98 7106 1568.07
    0.00    0  0.00   230.14 7051 1584.68
    0.00    0  0.00   223.98 7170 1568.28
   17.66  171  2.94   219.54 7169 1536.96
   37.56  144  5.28   222.41 7146 1552.05
   53.41  184  9.57   203.01 5774 1144.77
  127.98 4969 621.06   119.78 5393 630.85
  127.98 5573 696.50   127.71 5592 697.37
  128.00 5758 719.77   125.87 5858 720.02
  128.00 5513 689.17   127.32 5542 689.12
  128.00 5992 748.97   128.00 5992 748.97
  128.00 5459 682.40   128.30 5504 689.62
  128.00 5854 731.70   128.00 5846 730.70
  128.00 5589 698.61   128.00 5605 700.61
  128.00 3684 460.50   127.90 3671 458.52
  124.39  547 66.45    97.00  740 70.13
  128.00 5623 702.93   128.00 5620 702.55
  128.00 5803 725.37   128.66 5849 734.87
  128.00 5638 704.77   128.00 5642 705.27
  128.00 5922 740.24   128.00 5918 739.74
              disk1               disk0
    KB/t  tps  MB/s     KB/t  tps  MB/s
  128.00 5648 705.98   127.93 5639 704.49
  128.00 5946 743.25   127.98 5951 743.79
  128.00 5649 706.14   128.00 5645 705.64
  128.00 5876 734.54   127.94 5886 735.43
  128.00 5456 682.03   128.00 5457 682.15
  128.00 5874 734.22   128.00 5866 733.22
  128.00 5605 700.57   128.00 5615 701.82
  128.00 5727 715.91   127.91 5728 715.55
  108.45 1813 191.97   108.37 1806 191.09
    0.00    0  0.00     0.00    0  0.00

2. From external "regular" sata-ssd:
Code: 
mini-me@mini-fusion ~ % iostat -d disk1 disk0 1
              disk1               disk0
    KB/t  tps  MB/s     KB/t  tps  MB/s
    0.00    0  0.00     0.00    0  0.00
    0.00    0  0.00     4.00    5  0.02
    4.00    5  0.02    10.53   30  0.31
   66.00    4  0.26    96.71 2151 203.12
  128.00    8  1.00   128.49 4087 512.84
  105.82   11  1.13   124.62 4611 561.15
  128.00    8  1.00   128.00 4172 521.54
  128.00    8  1.00   128.00 4078 509.77
  128.00    9  1.12   127.95 4590 573.55
  128.00    8  1.00   128.00 4085 510.65
  128.00    8  1.00   125.44 4171 510.90
  128.00    9  1.12   127.97 4596 574.43
  128.00    8  1.00   128.00 4069 508.60
  128.00    8  1.00   129.42 4171 527.13
  128.00    9  1.12   124.65 4729 575.65
  128.00    8  1.00   125.39 4159 509.29
  128.00    9  1.12   128.00 4099 512.42
  128.00    8  0.99   128.00 4549 568.69
              disk1               disk0
    KB/t  tps  MB/s     KB/t  tps  MB/s
  128.00    8  1.00   128.00 4081 510.17
  128.00    9  1.12   127.94 4203 525.18
  128.00    8  1.00   126.86 4498 557.20
  128.00    8  1.00   126.66 4116 509.14
  128.00    9  1.12   128.00 4477 559.56
  128.00    8  1.00   128.00 4181 522.58
  128.00    8  1.00   128.00 4080 510.03
  128.00    9  1.12   126.02 4578 563.37
   89.78 1447 126.83   115.74 5745 649.36
  128.00 3091 386.32   127.47 7435 925.53
  127.86 4409 550.55   116.93 4956 565.94
  127.95 5196 649.31   128.06 5258 657.57
  128.00 5554 694.24   126.03 5646 694.85
  128.00 5270 658.70   127.98 5263 657.71
  128.00 5563 695.32   128.00 5559 694.82
  128.00 5317 664.68   128.00 5333 666.68
  128.00 5569 696.16   128.00 5559 694.91
  128.00 5263 657.90   128.00 5257 657.15
  128.00 5509 688.58   128.00 5523 690.32
  128.00 5350 668.77   128.00 5344 668.02
              disk1               disk0
    KB/t  tps  MB/s     KB/t  tps  MB/s
  128.00 5457 682.17   128.00 5463 682.91
  128.00 5288 661.06   127.98 5276 659.32
  128.00 5454 681.77   128.30 5515 691.00
  128.00 5253 656.65   127.98 5254 656.66
  128.00 5497 687.12   128.00 5502 687.74
  128.00 5191 648.89   127.90 5204 650.03
  128.00 5483 685.42   128.00 5485 685.66
  128.00 5347 668.43   128.00 5344 668.06
  120.90 4124 486.95   120.79 4114 485.33
    0.00    0  0.00     0.00    0  0.00

3. Copying within Fusion, well, I'm not sure how to do that since APFS just mirrors the file...
 
MayflyMaven said:
You're doubling your risk of data loss with this setup, if either one of those devices fails, you lose everything. Having an external device in the mix makes it even more risky – what happens if the device is accidentally disconnected?

You could get the benefit of both devices with less risk by moving your home folder to a volume on the external storage.
Click to expand...
Would you like to measure or quantify that "risk"?

Every mass storage has a risk to be destroyed at any given moment.

To remove that risk is to make backups.

I surely don't care if the risk is "once in 100TBW" or "once in 1000TBW".
The procedure is the same: backup.
 
Bigwaff said:
I assume you are trying to make an external USB SSD “faster”. If Fusion Drive external component a USB external SSD, would be interested in some read/write performance metrics.

Thinking you might be better served switching a brittle Frankenstein Fusion Drive set up to a dedicated Thunderbolt 3 external enclosure? Either way, different strokes for different folks. Carry on.
Click to expand...
External side is TB3. (That was mentioned in 1st post.)
Sonnet Echo Dual and the ssd in it is Mushkin Tempest ‎MKNSSDTS2TB-D8.
 
toke lahti said:
Would you like to measure or quantify that "risk"?
Click to expand...
It's at least "twice the risk". Probably more considering that one of the devices is external. It's hard for me to see the risk as "low" (or quantify it in terms of hours that you can expect to operate without device failure), I used to deal with hard drive failures as part of my profession so that seemed to happen all the time. To a doctor, everybody seems to be sick 🙂

toke lahti said:
I surely don't care if the risk is "once in 100TBW" or "once in 1000TBW".
The procedure is the same: backup.
Click to expand...

If you have a solid backup plan, I'm happy!
 
Houston, we have a problem!
1765379419808.png


...Aaand that problem went away with restarting the system...
 
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I tried to install Sequoia from thumb drive few times, but mini2018 just crashes and boots.
Since installation is done from "live" system, I guess there is no logs anywhere to see what caused the crash?

I can try again in about 10 days.

I want to have permanent "internal" boot partition, if some glitch occours in future, but I will try to use the whole internal ssd as part of Fusion, if that would work. After that it might be possible to downsize that and fit another parition or container that can be booted without external.

I ran Blackmagic's speed test with internal boot and fusion and there was some odd behavior, but I suspect that Mushkin tb connected ssd is very close to the speed of internal ssd.

So, this kind of Fusion would be beneficial with newer faster internal ssd, like M4-mini.
 
hg.wells said:
I would argue that using an external drive is more of a risk and if one drive dies data is likely gone from both.
Click to expand...
And then you replace the defect hardware and restore from backup.
Like you would, if you'd use just one storage and it dies.

It is kinda silly argument, that one is always good, but two goes always too far.

If Apple would have developed to other route it did, a mac could now have several internal nvme-slots, where you could hot swap storage. Of course they didn't. It's more profitable to sell new macs and iCloud.
 
Honestly, I would just use the internal as standard, and then just create a folder called "My Documents" or whatever on the external and put files and folders there. Files don't need to be in your user account.

The benefit of "one large volume" is not worth the risks of it being more fragile and more work.
 
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benwiggy said:
Honestly, I would just use the internal as standard, and then just create a folder called "My Documents" or whatever on the external and put files and folders there. Files don't need to be in your user account.

The benefit of "one large volume" is not worth the risks of it being more fragile and more work.
Click to expand...
I want to rebel against ssd's apple tax, so I'm not going to buy big enough internal even to my next DESKTOP mac.
Why would I?
It's a desktop device. There is no problem having accessories attached to it, there is plenty of them anyway.

I'm currently having my home folder on 2 external disks.
Next mac, maybe internal and external.
The problem is Apps (now 122GB) and Library (now 162 GB).
In 2nd external: Music is 250GB, Pics (464GB) and Movies (555GB).

I could use hours and hours to extract stuff from those, but I prefer to have big and cheap drives and not to waste my nerves thinking about storage planning.

Fusion drive was perfect for me, but seems to be that Apple still does not want me to use it.
But like with eGPU, they might come back someday.
The tools are there, they just need a bit tweaking from Apple's OS development team.

Back in 2019, I tried to expand the logical home dir to another drive.
Back then, when booting from external, you'd better have the OS installed in every external drive, since there were bugs in Recovery mode with changing safety settings, of which boot drives password it would accept. Maybe the firmware took it from internal, I don't remember sharply. But when I had that OS installed in 2nd drive there were problems with UID's and since Apple does not offer any support for using UID's and they try to hide it as deep as possble and their onion skin protections tend to forget basic multiuser unix enviroment, I thought it was best to forget about "the right way" to create multidisk home folder.
 
Last edited:
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