UASP (usb attached scsi) for external SSD not working in 10.15 Catalina

After the update to 10.15, I've found my external SSD drives dropped write speed from sustained ~480MB/s (Mojave) to sustained ~400MB/s (Catalina). I can only assume this 15% drop is because of lost of UASP support for external drives.

After checking extensions, IOUSBattachedSCSI.kext is shown "verifed" but "not loaded". And I cannot find a straightforward way to load it.

I'm running a 2018 mac mini, OWC usb3.1 gen2 dock, 50TB ssd drive (maxes out at sustained 500MB/s), and running Paragon NTFS (as all my SSD's are formatted NTFS).

Mac mini 2018 or later

Posted on Oct 14, 2019 2:28 PM

Top-ranking reply

Ducati9x Author

Level 1

5 points

Posted on Oct 15, 2019 8:28 AM

Found a solution from a knowledgeable Apple tech:

Must reset SMC chip.

Power off
Hold Ctrl+Shift+Option+Power button (keep holding for 10-15 seconds)
Mac will power on, then shortly power off
Release buttons
Remove power plug (remain unplugged for 15-20 seconds)
Reinstall power plug
Start as normal

Worked for me. Transfer speeds increased to 480MB/s sustained.

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UASP (usb attached scsi) for external SSD not working in 10.15 Catalina

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