r/OWC

I have just purchased an OWC Express 1M2 and populated it with a Samsung 990 Pro 4TB M.2 SSD.
I am on a Mac M1 Studio Max, using the rear thunderbolt ports.
I am running Tahoe 26.3.1

I have managed to copy a small amount of data onto it, but when copying many GB or files it routinely disconnects within about 30 seconds.
I can read files fine.

When I try and tun Apples Disk Utility and run a First Aid check, the drive will disconnect within about 30 seconds.

I have replaced the thunderbolt cable with a good quality third party cable, with no improvement.

Sometimes when I connect the drive, it can't even browse the contents.

Connecting it to one of the front USBC ports seems to work fine.

Could it be a power delivery issue?

Any ideas of what the problem could be?

I've been testing my SN850X + OWC 1M2 80 combo, vs various internal drives across my Mac Minis and Mac Studio. The external combo beats anything internal by a mile on almost every single metric, and especially on sustained activities.

I've switched to using my external combo as my main boot drive.

Just thought this might be of interest to those considering the newer model.

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Random I/O -- what makes your Mac feel fast

These are the metrics that matter for app launches, Spotlight, swap, and general snappiness. Higher is better.

Test	WD SN850X (Express 1M2)	Apple 1TB (internal)	Apple 2TB (internal)
Random Read 4K QD1	15,175 IOPS	13,109 IOPS	11,311 IOPS
Random Write 4K QD1	10,433 IOPS	7,746 IOPS	7,141 IOPS
Random Write 4K QD32	64,372 IOPS	38,769 IOPS	25,436 IOPS
Mixed R/W 70/30 QD16	99,700 IOPS	75,069 IOPS	68,590 IOPS

The external wins every random I/O test.

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Latency -- lower is better

p99 latency at 4K QD1. These are the micro-stutters you feel when the OS writes swap or logs.

Test	WD SN850X (Express 1M2)	Apple 1TB (internal)	Apple 2TB (internal)
4K Read p99	112 us	142 us	171 us
4K Write p99	180 us	305 us	1,630 us

The 2TB really underperforms on latency.

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Sequential throughput

This is where Apple's internal SSD wins -- large sequential writes. Higher is better.

Test	WD SN850X (Express 1M2)	Apple 1TB (internal)	Apple 2TB (internal)
Seq Read 1M QD1	4,538 MB/s	3,123 MB/s	3,106 MB/s
Seq Write 1M QD1	4,355 MB/s	6,062 MB/s	5,816 MB/s
Seq Read 1M QD8	6,639 MB/s	6,506 MB/s	6,688 MB/s
Seq Write 1M QD8	5,585 MB/s	6,897 MB/s	--
Seq Read 128K	2,160 MB/s	682 MB/s	728 MB/s
Seq Write 128K	2,118 MB/s	3,264 MB/s	2,984 MB/s

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Sustained write -- 5 minutes continuous

5 minutes of continuous 1M sequential writes with per-second bandwidth logging and SMART temperature monitoring.

Metric	WD SN850X (Express 1M2)	Apple 1TB (internal)
Avg bandwidth	5,284 MB/s	1,410 MB/s
Min bandwidth (1s sample)	4,091 MB/s	35 MB/s
Max bandwidth (1s sample)	5,669 MB/s	2,736 MB/s
Total data written	1,548 GB	413 GB
Mean latency	746 us	2,823 us
p99 latency	3,097 us	26,083 us
p99.9 latency	8,356 us	104,333 us

The Apple drive shows severe SLC cache exhaustion, and keeps crashing while it writes down. The WD maintains 5,000+ MB/s throughout with a gentle decline to ~4,900 MB/s.

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Thermals

Both drives' temperatures were logged simultaneously during each test to check for cross-heating through the chassis.

Metric	WD SN850X (Express 1M2)	Apple 1TB (internal)
Start temp	34C	33C
Peak temp	56C	71C
Temp rise	+22C	+38C

The Express 1M2's passive cooling keeps the WD at 56C under sustained full write load. The Apple internal hits 71C.