Internal 2.5" hard disk put in an enclosure vs. a ready-made external hard drive; and 3.5" external hard disks

I'm looking to buy a 640 GB - 1 TB external hard drive soon, and have a couple of questions regarding external drives:

Internal drive + enclosure vs. Ready-made external drive
I would like to ask if there are any significant differences (mainly in regards to power usage, transfer speed, risk of failure) between, for example, an internal Western Digital 2.5" hard disk & just buying a separate enclosure for it, vs. a Western Digital My Passport ready-made external hard drive? Don't factor in the free backup or encryption software, as I don't need or use them anyway.

2.5" Hard Drive Heights (9 MM / 12 MM)
I've read that there are some 2.5" hard drives have heights greater than the 9 MM standard (12.5 MM). If I buy a 12.5 MM-height hard drive, do I need to worry about it not fitting an enclosure? Or do most enclosures support the 12.5 MM heights? What 2.5" drive capacity usually has the 12.5 MM height? Do most 2.5" 1 TB drives have 12.5 MM heights? What about the 2.5" 640/750 GB drives?

3.5" External Hard Drives
Also, would you recommend a 3.5" external hard drive like WD Elements Portable (usually cheaper than its 2.5" counterpart)? Any significant downsides (power usage, performance, longevity, etc.) from getting an external hard drive like this (aside from the size)? This could be powered by a USB port source only, right?

 

No, needs to be plugged in to the wall.

Also, some premade enclosures for 2.5" drives nowadays have the drive permanently attached to the enclosure. You can't take off the USB connector and use it in your laptop.

 

Does this apply for all external 3.5" drives? Western Digital advertises WD Elements Portable (which I believe is 3.5") like this (screenshot):

I don't mind this as I'm only looking to buy an external hard drive not be used as an internal drive, anyway.

 

That's a 2.5" model for sure. 3.5" model linked here: http://www.wdc.com/en/products/products.aspx?id=260

3.5 drive without enclosure (approx):

 

I see. Looks like 3.5" is not an option for me anymore because of this. Thanks for that. (I thought that Elements was the WD external 3.5" product line while My Passport is the 2.5" line.)

 

if you have a spare 2.5in drive get a caddy off ebay
they can be had for next to nothing these days

 

I don't have a spare 2.5in drive. I'm just looking to buy an external drive (either internal + enclosure or a pre-made external drive).

The external drive I'll be using will be almost always connected to my laptop as long as it's on. Are there power usage differences like "idling" or "spinning down" when the drive is not being used when using a pre-made drive vs. an internal drive + enclosure? Or are they pretty much the same?

 

I got enclosure that fits only 9mm internal drives, but it's got eSATA port as well as USB, and a DC power connector. That eSATA port is priceless ... as long as you have that port on your laptop though. If not, do like me: buy eSATA Expresscard

HDD connected over USB is slow.

 

For the other half of the question, all current 2.5" drives 1 TB or greater are 12.5 mm or more (I heard 15 mm for the 2.5" 1.5 TB drive). The largest 9.5 mm drives currently are the Seagate and WD 750 GB drives, and the upcoming 7K750 from Hitachi. Since the Z5K500 is a single platter 500 GB drive, there are hopes that a 9.5 mm 1 TB drive are forthcoming, but none have yet been announced. Oh, and the 640 GB drives are 9.5 mm too.

 

Doesn't Samsung have a 1 TB 2.5" 9mm but its 5400 rpm?

 

Oh, yes, that's right, that was announced a few weeks ago (and is also not available yet). I forgot about that one. The Z5K500 is also a 5400 RPM drive (I vaguely remember seeing a 7200 RPM 7 mm 500 GB drive, but I can't seem to find any mention of one anymore), so if any possible Hitachi offering would be based off of that, it'd probably also be 5400 RPM. Of course, with the sale of Hitachi, it also may never come out...