Surprise, disk drives break a lot

| Comments (2) | Misc
Computerworld has a good article about hard drive failures. The bottom line here is that (unsurprisingly) real world drive failure rates far exceed the failure rates (MTBF and AFR) reported by manufacturers. This won't surprise anyone who has operated systems with a reasonable number of disks.

Fundamentally, though, what's annoying about disk drive failures isn't that they happen but that they're unpredictable. After all, the gas in my car keeps breaking—every three hundred miles or so I need to put more in—but that's not a big problem because I have a gauge that tells me when I need to refill the tank. If hard drives behaved the same way, you could just treat them as a consumable. The problem is that (as Pinheiro et al. report), disk drive failures are random and the SMART diagnostics don't provide reliable warning. Instead, you're left with failures as surprise events requiring emergency recovery. Even if you have backups, this kind of failure isn't fun, coming as it always seems to right when you're about to go home for the weekend.

The standard answer here is to use RAID and then swap the drives whenever one fails, but my experience (and that of other home users I've talked to) is that RAID systems fail to recover often enough on drive failure that you not infrequently end up with something that looks more like a backup and restore than an emergency replacement.

2 Comments

I think the problem with home RAID systems is that a) no one really knows when a drive fails, b) what do you do when a drive fails and c) home RAID systems are not of the same quality as business RAID systems. Besides most people don't have the technical knowledge to deal with it so what's the point?

I have a terabyte of available space in a RAID-5 configuration. A drive failed and the automated e-mail alert system built into the drivers did exactly nothing. And since HD capacity changes so rapidly I couldn't find a HD in the same capacity so now I have a 100 gigs wasted on one of the disks.

And yet HDs work well enough that we are shoving them into all sorts of devices. In my living room I count 5 devices with a HD (excluding my laptop).

What I want to know is what special incantations they used on the hard drives they used in the original TiVo. Mine is still going strong after , what, nine years? I think I've gone through at least three hard drives on my desktop in that time and TiVo is certainly more hard drive intensive than typical desktop use.

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