I’d estimate that about 50% of my external hard drives fail over their useful lifetime. The manufacturer doesn’t seem to matter a lot. Lacie, Western Digital, Maxtor, etc. I’ve tried them all and they all fail. Multiple redundant backups, and close attention to signs of problems are necessary to maintain data. And yet to date I think I’ve had exactly 0 hard drives replaced or repaired under warranty. Why? It simply isn’t safe to send hard drives back for replacement. Today’s multi-terabyte drives, and really any drive, contain too much personal data to let it out of my sight; at least not without running it through a degausser that costs as much as several dozen replacement drives first.
Once an external hard drive has failed, it is usually not possible to erase it, much less securely. However the most common mode of failure for an external hard drive seems to be that the enclosure fails, but the data on the platters is still there and can be recovered with enough effort and tools simply by pulling the platters out, and shoving them into a working enclosure. It’s not something I would usually do unless I didn’t have backups. However more often than not it’s something that could be done, either by someone who intercepts the package, a tech working at the hard drive company I return the drive to, or the next warranty servicee who gets back a reconditioned drive with my data still on it. Usually they’d have to use a disk recovery tool to see that data, but sometimes not even that. One third party Mac repair shop once sold me a “new” hard drive that came complete with the contents of someone else’s system: Quicken files, college essays, personal letters, etc.
I recently had the uncommon experience of getting enough warning to erase a hard drive before it failed completely. One of the Western Digital Elements 2.0 TB USB drives I use for rotating Time Machine Backups began making a whining noise. That’s a pretty reliable sign of imminent failure. For a little while, it wouldn’t mount at all, but after some coaxing I got Disk Utility to recognize it and did a single pass erase with all zeros. After that, I was reasonably comfortable sending it back for replacement under warranty. I paid for postage, but otherwise, Western Digital made the process relatively painless. I just entered my serial number in an online form, entered a reason for return, and they gave me a shipping label. I packed the drive up, took it to the mail room, and sent it off. And then a week later they sent me back the wrong drive.