3.5" HDD over USB 3.0 - Read/Write speed dropped by 75% after Win 8.1 clean install - Cause? Fix?

[DevillEars]

I recently migrated from Win 7 to Win 8.1 on a desktop system comprising:

Asrock Fatal1ty Z77 Professional
Core i7-3770
16GB G.Skill Ares DDR3-1600 CL9
Corsair AX850

Attached to one of the Z77 USB 3.0 ports is a Lian-Li EX-203 2-bay enclosure with 2 x Seagate ST3000DM001 drives.

Initially - after initial Win8.1 install - I was surprised to be getting very fast copies to/from these external drives (~150 MB/sec). I then ran CrystalDiskMark on the drives and the results were in line with Windows Explorer file copy rates (~155MB/sec read / 145 MB/sec write).

After some malware sneaked past Windows Defender and nailed the system, I did a complete clean re-install of Windows 8.1 and replaced Windows Defender with Norton Security 2015.

Suddenly, the copy rates to/from these same drives attached to the same USB 3.0 port are yielding copy rates of ~40MB/sec (confirmed by CrystalDiskMark).

MY QUESTIONS:

a) What could have caused this 75% drop in copy rate? (a driver somewhere? a setting?)
b) How can I get this copy rate back up to where it was?

BTW: Malware that caused hassles (Lavasoft and Web Companion) both came courtesy of a CNet download that Windows Defender missed... 🙁

Any solution would be greatly appreciated as I was just getting used to this lightning-fast USB 3.0... 🙁

Regards,

Dave

 

[geofelt]

Is there a motherboard specific USB3.0 driver?
Try installing from your motherboard driver cd.

 

[DevillEars]

All the latest level drivers were downloaded from Asrock website and installed immediately after Windows 8.1 clean install. Also, I've checked the BIOS entries and all USB settings are correct.

BUT, THE PROBLEM HAS BEEN RESOLVED (BUT I DON'T KNOW WHY IT WORKED)...

I switched the USB 3.0 port used and the speed went back up to ~150MB/sec. I then "safely removed" the enclosure and plugged it back into the same port as originally used and - voila! - it stayed at the high performance level.

So, that's the "WHAT" was done - can anyone come up with a "WHY" it slowed down and why it came back again?

I'm puzzled... (but happy... )

Dave