I just bought a western digital my passport essential 160 gb external usb HD. It came pre-formatted fat32. After a few frustrating weeks with fat32's file size limitation, I re-formatted it to ext3.

My question is: Does formatting this hard drive (or any HD) affect its built-in spindown capability? This HD was spinning down before I formatted it, but I was never really sure how long it took. Now, after formatting it, it's been idle for about 10-15 min. and is still spinning. I don't think it spun that long before, but I could be wrong.

Is this a desktop or a laptop ? I hope you know that HDD lifetime is measure in spin-ups the more spin-ups you do the closer the drive is to failure. On a laptop this is not much of a problem because laptop HDDs are rated in the hundreds of thousands of spin-ups specifically because spinning down a drive is a power saving feature, but desktop HDDs are rated in only tens of thousands of spinups, so don't try spinning down the drive on a desktop. If you want to control spin-up/down try looking into 'laptop-mode'.

Not that I could determine. According to Western Digital's website your hard drive spins down after 10 minutes of inactivity which is built in to the drive and can not be deactivated. My initial SWAG would be that with a different file system the drive may not be able to detect inactivity and therefore never spins down.

Yes, one specification is start/stop cycles. Since this is a portable drive I would guess it probably on the order of >100,000 times. The only failure data that WD actually prints is a 5 year life and an annualized failure rate of 0.8

Thank you both. I think it did finally spin down, but now it is spinning for no apparent reason. Since it is portable, I have another question: Must I wait for it to spin down before I disconnect it?

You have to unmount it before disconnecting to make sure all cached data is written properly. EXT3 filesystem will not let it spin down, I believe journal refresh is in every 5 seconds or something close to it. I'd consider EXT2 instead, no need to reformat, just convert it with tune2fs.

Your correct the commit interval default is 5 seconds which is reason the drive will not spin down.