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MacBook Pro eSATA with Mercury Extreme SSD
The 200GB OWC Mercury Extreme solid state drive (SSD) is as fast as it gets for any single device, so these graphs represent the fastest possible results you’ll get with eSATA on the MacBook Pro with any single drive.
Analysis
Read performance is fast with the OWC Slim and Sonnet Tempo Pro, but the Sonnet Edge lags considerably, though still much faster than Firewire 800.
Since the drive itself is capable of ~260MB/sec for reads and writes, it’s clear that the ExpressCard/34 slot itself is responsible for the slowdown.

Write performance has always been impaired with eSATA through the ExpressCard/34 slot, and runs here at less than half the potential speed (260MB/sec) of the OWC Mercury Extreme SSD. Still, it’s much faster than Firewire 800.

Apple 16.2" MacBook Pro with M1 Max Chip (Late 2021, Space Gray)
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