First published: Dec 2, 2008, 10:26am -0700
Last edited: Dec 3, 2008, 1:44pm -0700

Back the F:\ up!

Hard drive primer

First, a bit about how hard drives work.

A hard drive is simply a circular disk (or a collection of them), kind of like a CD, except the data is stored magnetically instead of optically. To read the magnetic data, a little arm with a magnet on the end sticks out over the disk while the disk spins. The little arm reads data off the disk as the disk spin past.

The disk is moving very fast (common disks spin at 7,200 rpm, or about 86 miles per hour at the edge of a 3.5” disk). The arm is also very close to the disk (the head of the arm is 3-7 millionths of an inch away from the disk in modern drives, floating on a pocket of air). Scaled up, hard drives move at speeds similar to an airplane traveling nearly 16 times the speed of sound (mach 16) a width of a human hair (18 micrometers) above the ground!

So, as you can imagine, the worst thing that could possibly happen to a hard drive is for this drive head to crash into the disk, destroying your ability to read the data and scratching up the disk platter. I suppose it’s worse if you shoot the drive with a shotgun.

But only barely.

It’s very hard for hard drive manufacturers to make disks that don’t crash when they’re dropped while spinning. They try, but it’s just hard to do. Recent laptop drives have gone as far as putting motion detection in so the drive head can be locked away from the disk platter if the drive detects that it’s falling. Laptop makers generally recommend that you keep your laptop off (thereby locking the disk head) during any traveling. I sort of think that’s silly though. What’s the point of a laptop?


So, this week, my sister’s laptop suffered an untimely and completely accidental calamity. As the laptop hit the ground, I thought, “boy, it’s a good thing it’s off.”

It wasn’t.

Then I thought, “boy, it’s a good thing her brother works for a backup company and backed up all her homework for her.”

I didn’t.

I mean, I work for Mozy, but I’m one of those crazy Linux guys, and Mozy currently doesn’t have a Linux client. As a result, I don’t use Mozy on my own laptop, and therefore often forget to recommend it to others. I’m a big fan of the adage “practice what you preach;” in this case, I argue software companies should eat their own dogfood and use their own products. Whoops! I guess I’m the odd man out here. I am totally practicing some of the things I’m preaching already: building incredibly distributed, fault tolerant, relational metadata management systems to increase performance for Mozy’s backend is fun! But I haven’t been practicing or preaching “Back the F:\ up!”.

Well, this week, that changed. Be safe, use Mozy.