[Updated this review on 28-Jun-2011]

I have purchased 4 of these Western Digital Studio II external hard drives over the past 18 months (three of them are 4TB, one of them is 6TB), and they are great. The first 3 of these I bought have been chugging along with constant use for more than a year, with nary a hiccup. I just purchased the 6TB model about a week ago, and it looks identical to the 4TB models -- I have high hopes for it as well.

For some context: In the past, I purchased 2 Iomega external drives and 4 LaCie external drives, and ALL of those external drives completely failed after a few months of use, while connected to 3 different computers. Unbelievable! But these Western Digital Studio II drives are a dream. They keep going and going...

These Western Digital Studio II drives have a choice of 4 different interfaces (USB 2.0, FireWire 400, FireWire 800, and eSATA), and I've used them with all of the interfaces. I've also used them on Windows Vista and Windows 7 (both 32-bit and 64-bit), on three different computers. No matter which interface you use, or which version of Windows, they work right out of the box, are immediately recognized by Windows, no drivers needed. No fuss, no bother, no reading the user manual, etc. (You just need to remember to format the drive for Windows; see below.)

Over the past 18 months or so, I have discovered some technical tidbits about using these drives that I wanted to pass along, because it might help someone who is stuck. Most of this information applies to any large external drive that you attach to a Windows computer; this info is not necessarily specific to these Western Digital drives.

So, here are some technical tips when using these Western Digital My Book Studio II drives:

1. When you receive the drive, it is formatted for the Mac, rather than Windows. No problem, you just need to format it for Windows, which takes less than a minute. IMPORTANT: When you are formatting the drive for Windows, you MUST use the USB 2.0 port on the drive (with a USB 2.0 cable -- included with the drive) to format it. After that, you can use any of the interfaces (USB 2.0, FireWire 400 or 800, or eSATA) to access the drive. If you try to format the drive while connected to your computer with eSATA, your computer will only see about half of the drive's capacity. Again, this only affects initial formatting. After formatting, use any interface, and your computer will see the full capacity of the drive. HOW TO FORMAT: Choose Start, right-click on Computer, choose Manage, and select Disk Management. You probably know the drill from there, but if not, see the documentation that comes with the drive. Do a "Quick Format" -- no need to do the lengthy normal format.

2. The fastest port on these drives is the 3Gbit/sec eSATA port. If you only have one eSATA port on your computer, and you have more than one of these drives (like me), you might think you can use an eSATA external port multiplier to turn your one eSATA port on your computer into multiple eSATA ports so you can connect multiple external drives to one eSATA port on your computer. However, this only works if the eSATA port on your computer supports an eSATA port multiplier. Some computer eSATA ports do not (for example, I have a Dell XPS 17 laptop, and its eSATA port does not support an eSATA port multiplier). If you are in this situation, or if you don't have any eSATA ports at all on your computer, but you DO have a USB 3.0 or SuperSpeed USB 3.0 port on your computer, you are golden. You can use a StarTech.com USB3S2ESATA 3 Feet SuperSpeed USB 3.0 to eSATA Cable Adapter or similar product, which is a USB 3.0 to eSATA adapter cable, to connect the eSATA port on your external drive to the USB 3.0 port on your computer. Most USB 3.0 ports run at 5Gbit/sec, and even though most eSATA ports only run at 3Gbit/sec, this adapter cable lets you use the drive at 3Gbit/sec from your computer's USB 3.0 port, which is 6 times faster than the slow 480Mbit/sec speed of a USB 2.0 port connection.

3. I discovered, on my computer, that when I attached one of these drives to my laptop computer via my computer's eSATA port, that my computer would no longer reboot successfully, unless I unplugged the eSATA cable and plugged it back in after my computer got past the initial stages of rebooting. This is not the fault of the drive. As noted on the Western Digital knowledge base on their web site, the BIOS of many computers cannot recognize hard drives larger than 2TB (even though Windows Vista and Windows 7 can recognize much larger drives), so the BIOS stops rebooting when it sees my huge 4TB or 6TB drive plugged into the eSATA port on my computer. I rebooted my computer and pressed F12 to change the "Boot Order" on my computer, but there was no way to tell the BIOS NOT to look at the eSATA port when rebooting. However, my computer BIOS DOES let me tell it to ignore the USB 3.0 ports on my computer when booting. So, I plugged my 6TB (or 4TB) drive into my computer's USB 3.0 port, using the above USB 3.0 to eSATA adapter cable to connect to the drive's eSATA port, and told the BIOS boot order on my computer to ignore the USB ports, and now my computer reboots fine when my big Western Digital 4TB and 6TB drives are plugged into it. Plus, it still has 3Gbit/sec transfer speed, which is great.

4. With Windows 7 (and perhaps with all versions of Windows and Macs, I'm not sure), these external drives will go to "sleep" after somewhere around 15-30 minutes of inactivity. In theory, this is not a problem, because the next time you try to access the drive from Windows, the drive will automatically spin up, and about 10-15 seconds later it will respond as normal. However, it takes sufficiently long for the drive to "awaken" from sleep that Windows 7 sometimes records the drive as no longer available, until you unplug and re-plug the power to the external drive. There is a little bit of discussion about this problem on the Internet. No one seems completely certain why the drive goes to sleep (is the it the firmware in the drive, or is it a "sleep" command from Windows 7?) and there does not seem to be a consensus on how to solve it -- different people offer different solutions. However, I wanted to share the solution that I found for this problem, if you are using the external drive via the USB port (or via the drive's eSATA port going to a USB 3.0 port on your computer using a USB 3.0-to-eSATA adapter): Under Windows 7, go into the Control Panel. At the top right of the screen, choose "View by: Small icons." Click on "Power Options." Look at which "power plan" you have selected (that has the radio button selected), and click the "Change plan settings" to the right of that. On the next screen, click on the "Change advanced power settings" link, toward the bottom. In the next dialog box, scroll down and click the "+" next to "USB settings." Then, beneath that, click the "+" next to "USB selective suspend setting." Change the "Plugged in" setting to be "Disabled," and if you also use these external drives on battery power, change the "On battery" setting to also be "Disabled." Then, click OK to close the dialog box. Making this change to the Power Options under Windows 7 seems to prevent Windows 7 from putting the external drives to sleep. Alternatively, other people have had success using a free utility called "xSleep" at [...]that periodically accesses your external drives so they won't go to sleep under any version of Windows (and you can put it on a schedule, so the drives can go to sleep at night, for example).

I hope the above info is helpful to someone. These Western Digital My Book Studio II drives are awesome.

I bought my Western Digital My Book Studio II - 4TB (2 x 2 TB) USB 2.0/FireWire 400/800/eSATA Desktop External Hard WDH2Q40000N with great expectations. Upon arrival I immediately reconfigured it to be RAID 1 mirrored (2TB the raw usable) for the added storage safety. Things went swell for about 58 days with it hooked up to my new iMac 27" i7 computer. I used it to put my /User directory onto to store my roughly 1.3 TB of files, music, videos, etc.

Suddenly about 60 days into usage my iMac seemed rather slow. Eventually I realized it was various programs trying to save data to this external RAID 1 unit. After they all eventually wrote what they had to and shut down, I rebooted my iMac. This external Western Digital RAID 1 array did not remount. I was sort of freaked out!!!

I did some online research and sure enough various websites contained other users' experineces with this device frying its logic board within the first 90 days or so. I immediately ordered a NewerTechnology Voyager Q hard disk "toaster" intending to open up the Western Digital unit and pull both hard drives out to hopefully find at least one in good condition and then continue use of my computer and files.

I received my Voyager Q, opened up the Western Digital external RAID 1 array and pulled drive "A" from it and slapped it into the Voyager Q. It mounted right up in the finder and a disk utility disk check showed it to be clean. All files were as I would have expected. I have not touched drive "B" inside the Western Digital unit since drive "A" was fine. Drive "B" now stands temporarily as a mirrored snapshot in time at the point of the Western Digital enclosure failure.

I may have the enclosure replaced under warranty by Western Digital, but I have lost confidence in relying on this device for long term use so do not see the point at this time. My new plan is to order a second Voyager Q and move to a weekly bitwise disk clone using SuperDuper. I will also add an extra Western Digital 2TB Caviar Green drive (same as the two in the failed enclosure) and rotate the two extra week to week in the cloning process. This will allow me to also keep one clone offsite for extra safety. I have nothing bad to say about the Western Digital 2TB Caviar Green drives only the supplied enclosure.

I rated this device 5-stars for Data safety since the RAID 1 mirroring seemed to work up to the bitter end of the enclosure and my data was in good shape - give credit where credit is due... For Longevity and Trustworthy I can only give the lowest 1-star rating due to the events described above. I give 2-stars for Reliability since it did work as expected for about 60 days and it did not corrupt my data upon death.

I really wish this device had lived longer (at least beyond the warranty period) as a "professional level" RAID array such as those available from QNAP and others are significantly higher in entry price. In the long run I will likely move to a QNAP 6-Bay iSCSI SATA Dual-LAN Network Attached Storage TS-659-PRO+ setup as a RAID 6 array after I become weary of the planned intermediate disk cloning solution to data safety.

Best wishes to Western Digital who's hard disks I have used, and continue to do so, over the years. I hope they eventually figure out why these RAID enclosures are dying prematurely.

*** Update 1/25/2011 *** I removed drive "B" from the WD enclosure today to begin using it in the drive cloning process described above. Unfortunately it is unusable. A disk check on it showed "bad node structure". I tried to repartition and reformat the drive using disk utility to no avail. All attempts ended in failure to partition or format the drive. I ordered two new WD20EARS drives from Amazon today so that I may clone the working drive "A" data onto the two new disks and arrange for this enclosure and its two supplied drives (WD20EADS drives it turns out on inspection) to be returned to either the manufacturer or Amazon for replacement or refund. A not so satisfying end to this saga - but so far I have still not lost any data!

Update: I actually have really under appreciated this drive. I did not even realize you can swap out the hard drives in it (easy!) for bigger drives. I called WD and they said use only the WD Green drives and only up to 3 TB per unit. So it can be upgraded to 6 TB for a couple hundred bucks! That is a good deal.

Also, my iMac is still going on quite well. I don't see updating it for a couple more years (its replacement by Apple was also stripped of some things I like - hopefully Apple sees users want those things in next revisions). Anyhow, the 11,1 iMac's fastest external is FW 800 and it has worked well for me.

WD seems to have stopped making this device except one that is USB 3 only or Thunderbolt. There is no way to buy a Thunderbolt drive and plug it into FW or USB with some kind of adaptor. It is impossible. BUT it is possible to get an adaptor and use a FW 800 drive WITH a Thunderbolt Mac.

I'd consider a USB 3.0 (it will work in 2.0 on my iMac) but, the USB on my iMac has been kind of funky. I have to be careful to not overload the USB. Unplug some things I don't use when using other things. So USB is out as an update option on external expansion.

In the updated new drives I am adding, I am doing a mirror set up so I have redundancy. I used this drive first with Snow Leopard then, strait to latest Mavericks (I skipped the Lions). No problem with any of these and I did not do the firmware update. I might have to in order to use the 3 TB drives I am adding. Check with WD first.

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It has held up very well (so far). Albeit, it does not get much action, mostly sitting, on, waiting to be awoken in the morning, and occasionally accessed or written to. Sometimes, used to back up something.
Eventually, I'll relegate it to only back up duty or as an NAS drive.