There’s no shortage of external USB drives, so the differences in models often comes down to how many ports they have and how compact they are. But up to now they’ve all been restricted to USB. 2.0 which, while no slowpoke, is still a lot slower than Firewire.

But now we’ve USB 3.0 — whose transfer speed is up to 10 times faster than that of 2.0.That’s in a perfect world which doesn’t exist of course, but you wouldn’t be wrong saying that in general 3.0 is going to beat the pants off 2.0. Of course that does rely on the computer the drive is being used having a USB 3.0 port.

So one shouldn’t be blindsided when approaching reviewing an external drive that has USB 3.0 integrated inside. While the speed is probably the most important thing in many minds, don’t discount other factors of the drive that influence its use — for example, how well its outer chassis can handle being knocked about and how much protection it is affording the internal mechanism.  Or how convenient it is to use.

So we have to approach the Mercury On-The-Go Pro P/N MS8U3H7500GB, from the “outside” first, before being dazzled by how it handles data. That’s only fair when you’re spending $137 to get 500 gigabytes of storage in a Serial ATA drive spinning at 7200 rpm (with a 16mb cache)that weighs in at 2-1/2 pounds and is less than 6-inches long.

To start, the Mercury On-The-Go Pro is a looker — what else can you say about a clear acrylic case with bluish highlights (lit by the blue LED indicating the drive is active) that lets you see its “guts?” That the case is made from a polycarbonate material that is inherently shock-proof should enable it to deal with the bumps and thuds that are encountered in “real” use, day in and day out. Part of the whole “portability” thing is that the drive won’t be staying in one place all the time, but will most likely be taken with you or at least moved about your home as needed. That gets easier since it can be bus-powered so as to avoid the need of an AC adapter. But since AC power is available, those who want the most consistent use should op for this.  True you have to go and buy the adapter yourself (the product page has a link to the adapter under “Recommended Items”). But do keep in mind that the included case isn’t prepared for carrying an adapter around as well.

The other ports on the back consist of two Firewire’s 800 sockets (so you can daisy-chain) and a tiny power switch (big fingers, beware). Lastly there’s a USB 3.0 port on the Mercury On-The-Go Pro. A cable is included for this as well as for the Firewire socket,  which is good, but if you don’t have at least one backup USB 3.0 cable, go buy one. Better safe than sorry.  And just in case you didn’t know already, the USB 3.0 port is backwardly compatible with 2.0. Obviously that means if you connect the On-The-Go Pro to USB 2.0 you’re not getting 3.0 speed, but being able to tap into 2.0 is not just good insurance, but plain good sense to have.

Now the 500 gigabyte Mercury On-The-Go Pro P/N MS8U3H7500GB’s storage capacity is rated as following by the folks who make it: up to a half million photos, 250 DVD movies, 38 hours of digital video or 175,000 MP3 songs. Based on this, it should be obvious that using the drive to do a backup of your operating system, while having room left over to hold some files independently shouldn’t be much of an issue. That is unless you’re going to be taking it around with you instead — something that the drive is seriously intended for.

Now the selling point of the Mercury On-The-Go Pro, as it impacts PCs, isn’t the Firewire ports but that USB 3.0 port. To test the difference  — which is to say the speed overall — we’ll transfer files from one place to the other and then back again. Called into use is a PC running Windows 7, and the DiskBench benchmark program. A 500MHz Intel Pentium III CUP w/128MB RAM is the minimum needed, but this is a new PC just custom built so no worries there. Meanwhile the computer will be “idle” in that only the benchmark program will be active for the tests and no other external drives plugged in.

So here’s the specifics: we’ll transfer a file and then a folder of files from the computer’s hard drive to the USB drive, and then reverse the process to return the files back to the computer. This will be done using the USB 3.0 port specifically. Then this will be repeated, only it will be the USB 2.0 port that is used. In order to average the tests out, each test will be performed three times.

USB 3.0
Large file (aprox. 740 MB)
Internal to external — 6.0 sec, 6.2 s, 5.7 s – avg. = 6.0 s (rounded to nearest tenth)
External to internal – 6.2, 6.3, 6.0 – avg. = 6.2 s (rounded)

Multiple small files in a folder (aprox. 3.1 GBs worth of 3 MB photo files)
Internal to external – 29.8 s, 30.2, 30.3 – avg. = 30.1 s
External to internal – 52.3, 53.3, 53.0 – avg. = 52.9 s

USB 2.0
Large file transfer:
Internal to external – 24.5, 24.3, 24.3 – avg. is 24.4 sec
External to internal – 21.3, 21.4, 21.4 – avg. is 21.4 sec

Multiple small files in a folder:
Internal to external – 125.5, 145.2, 145.5 – avg. is 138.7 sec
External to internal – 112.4, 112.7, 112. 0 – avg. is 112.4 sec

Now here’s an odd thing — on the multiple small file test, the first transfer was slower than subsequent transfers, which were always incredibly fast.  A theory as to this is that this is because after the first transfer, the external drive was caching the file in memory (or causing the computer to cache it).  In any event, what I ended up doing was to power cycle the hard drive after every test to eliminate any effects of local file caching.

But getting back to the tests, as can be seen above, the results are dramatic and conclusive. What we can take away is obvious — that a USB 3.0 drive’s data transfer rate is significantly faster than that of 2.0. You only have to look at the numbers and compare them to see this difference starkly presented. You can see how much slower USB 2.0 is, especially for multiple small files being transferred from one folder to another.

Now it’s fairly obvious that using the Mercury On-The-Go Pro drive will save you time — and if you’re doing work on your computer to make a living, time saved can turn into more money earned. Those doing graphics will find the drive a fast alternative to having imaging stored on an internal drive — graphic manipulation of an image or video profits from speed that translates into actionable states from photo or video editing software, for instance.  It’s not always just about transferring files to/from the computer.

Editor’s Rating:

Rating: ★★★★☆


Review of OWC Mercury On-The-Go Pro P/N MS8U3H7500GB Review by
Bottom Line:
4.0/ 5.0
As expected, the 3.0 speed of the Mercury On-The-Go Pro  P/N MS8U3H7500GB  makes it highly useful because the speed cuts down working time and waiting time. Add a cool looking case (which took a few knocks without incident) and it’s hard to find any fault — other than those 3.0 ports are still a bit few and far between.


  • Lifetime technical support
  • Utility software disc included
  • Pouch and cables included


  • Power switch a bit tiny for large fingers to easily use

Marshal Rosenthal

Marshal Rosenthal is a Los Angeles-based freelance writer and journalist specializing in technology, consumer electronics and pop culture.