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2023 Mac Pro M2 Ultra: pair of OWC Accelsior 8M2 does 40 GB/sec?

re: OWC Accelsior 8M2 and OWC Accelsior 4M2
re: PCIe SSD

re: 32TB OWC Accelsior 8M2 PCIe SSD: Flawless Blazingly Fast Performance for Months

40 GB/sec (not 40 Gb/sec) is 8X faster than the entire bandwidth of the Thunderbolt 4 bus.

Thanks to OWC, I should soon have not just one, but two loaner OWC Accelsior 8M2 PCIe SSD cards totaling 16 NVMe SSD blades.

Get OWC Accelsior 8M2 at

Instant gratification takes too long, and 22GB/sec is just too slow... OK I’m kidding.

I/O speed of 22GB/sec is the entire memory bandwidth of my 2019 iMac 5K!

So I figured if 20 to 26GB/sec is possible with one card and the machine has two 16X PCIe slots, it would be a shame to not give dual cards a whirl.

Can the Mac Pro really really deliver 40GB/sec or more I/O bandwidth using two cards?

Practical limits

And how fast can IntegrityChecker Java go, given that its raw SHA512 capability is ~29GB/sec? Less than that, because of CPU load from I/O, and the I/O itself uses as much or more of the memory bandwidth as the hashing. Testing with icj and file system caching shows that 21 GiB/sec (22.5GB/sec) is the practical limit on M2 Ultra, barring some optimization I have yet to find in an already highly optimized and scalable program. Such speeds do require using larger I/O buffers of 32MB insted of 1MB.

50 files 107.4 GiB @ 21501 MiB/sec

macOS Ventura: hashing performance for SHA512, 1..24 CPU cores
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