NVMe+SATA RAID0 Late 2013-Mid 2015

[cyberstudio]

The observation is that PCIe 2.0 x 2 lanes (10Gbps) is not that much faster than SATA 3.0 (6Gbps) and Late 2013-Mid 2015 iMacs have both. (Mine is a 21.5" Late 2013.) So I picked up a WD SN750 500GB and paired it up with a Samsung 850 EVO 500GB, using RAID Assistant with a stripe size of 16K.

Apple does not allow a fresh macOS install on AppleRAID, so we have to restore from a Time Machine backup or use SuperDuper or Carbon Copy. Everything appears to run fine, except that I can't open any dmg, bz2, pkg and it says the file is damaged and should be moved to Trash. This is Catalina 10.15.7 and I tried both restoring from TM and using SuperDuper to clone a fresh install. I can open dmg's with Disk Utility, just can't double click. All preexisting Apps continued to work. Took me a few days of down time...

sudo spctl --master-disable didn't help, but csrutil disable in Recovery fixed the error. I can't install any security updates though. SIP is not happy with booting from AppleRAID.

A clone of a fresh install of Mojave 10.14.6 (APFS) did not even boot. Haven't tried HFS+, though.

A pair of SATA SSD's has always been working fine on my Mid 2010 27" with High Sierra.

 

[cyberstudio]

Well, I gave up and went back to single NVMe drive and removed the SATA SSD. Learned the hard way that the 3 of them: APFS+AppleRAID+boot, cannot coexist. Pick any two.

However this technique is still good if we stick with High Sierra HFS+. Or when there are no longer any more security updates for Catalina and we are willing to disable SIP.

 

[Amethyst1]

The observation is that PCIe 2.0 x 2 lanes (10Gbps) is not that much faster than SATA 3.0 (6Gbps) and Late 2013-Mid 2015 iMacs have both.

What kinds of speeds were you getting from the NVMe SSD alone, just out of interest?

Another thing to try (no idea about bootability though) is a RAID 0 of an internal NVMe SSD and an external NVMe SSD hooked up via Thunderbolt. This would need an NVMe TB3 enclosure with an external power supply or a powered TB3 dock (since the adapter can't supply power) and the bidirectional Apple TB3-to-TB2 adapter.

 

[cyberstudio]

The slower SATA drive helped sequential performance a bit but actually lowered the average random performance.

RAID0 was worthwhile for my Mid-2010 because HFS+ High Sierra booted flawlessly, its interface was a measly SATA II 3.0Gbps, but there are 3 of them including the optical drive, and everyone had a few too-small-to-be-useful SSDs from years ago sitting in a closet that can be combined to give a larger capacity.

My experiment was a failed one. A single NVMe, like this SN750, with the latest boot ROM, was the way to go. I have not encountered any stability issues so far.