Macs have had hard drives for nearly as long as Macs have been available, as is true of PCs, and a lot of those very early hard drives didn’t have great life expectancies. In addition to higher capacity and lower cost per data unit, hard drives have become far more reliable than those from the 1980s. But how long do modern hard drives really last?

That’s the question Backblaze has begun to answer in a recent blog post. Backblaze provides online data backup services and has over 25,000 hard drives running 24/7 to store that data. At this point, they’ve only been tracking this information for four years, so we don’t know how much longer drives may last, but it’s a good start.

Drives fail for one of three reasons: manufacturing defects, random issues, and wearing out. With its server drives running 24/7, Backblaze’s drives are probably going to fail sooner than if they were in a business or home computer where they might be running 8-12 hours a day – or even less if you let the drives spin down when not being accessed.

If anything, the Backblaze data is a worst case scenario. On top of that, Backblaze doesn’t use costly server-grade hard drives. Instead, they buy the same consumer drives you might add to your desktop or laptop computer.

What Did They Learn?

Looking at four years worth of data, Backblaze discovered that there are three failure periods, each with a different failure rate. There is a steady decline over the first 18 months, a period of relatively slow decline over the next 18 months, and a period of more rapid decline after the third year in use.

In brief, about 98% of new drives make it to installation, and approximately 94% remain in service at the one year mark. That drops to about 92% at the 18 month mark, and it almost holds steady for the next 12-15 months before starting to fall off again. At the three year mark, 90% of drives are still in service.

As the chart from Backblaze shows, things drop off rapidly beyond this point, so at the four year mark, about 78% of drives remain in use. If this nearly 12% failure rate continues, which is mere conjecture at this point, almost half of these hard drives will have failed by the six year mark. Conversely, over half of consumer hard drives running 24/7 for six years could be expected to remain in use.

This is pretty much in line with Google’s report Failure Trends in a Large Disk Drive Population published in 2007. Google reported an annualized failure rate of about 2% the first year, 8% over the first two years, a bit higher rate over the first three years, a decline over four years, and a bump upward over five. Interesting how there is little difference in the two and three year figures, just as in the Backblaze report.

That’s the 50-50 mark, and longtime computer users know that some drives last a decade or more in the real world – but then we don’t tend to subject them to the same kind of use as Backblaze does with its huge drive installations.

What Does It Mean?

Almost every new hard drive works out of the box, and about 95% of those should still be working one year later. Based on that, a one-year warranty seems like a pretty good bet for drive manufacturers, with an average of 6% of drives needing to be replaced within the first year. For you, it means odds of your drive failing during that first year are pretty low – no excuse for not backing up, but it should provide peace of mind.

The cost of extending that warranty to three years isn’t so big. Again on average, about 8% of drives will fail and need to be replaced. You can be pretty confident that your hard drive is going to last at least three years, but again don’t get too complacent and forget to backup.

After that, failures accrue at 11%, which is why five-year warrantys are rare on consumer grade hard drives. After the third year, you’d better have a backup plan implemented, and there’s an almost 50% chance that by the time it’s six years old, your drive will be history.

What It Doesn’t Say

Backblaze hasn’t said a thing about brands or drive capacities or any other factors. Neither does Google’s report. Your best bet is to find a local tech and ask them which drives they replace most often – and avoid them.

Backup Strategies

Bootable Clones

For years, my strategy has been to clone each of my hard drive partitions to a partition on a different drive, so if the first drive fails, the second is relatively up-to-date and able to take over. Historically I’ve bought two matching drives at the same time so I could partition them the same way and have matching capacities. As long as one of those drives is in an external enclosure, odds of them both failing at about the same time are slim. Then again, I often have both drives in the same machine, which means they are both wearing out at a similar pace. Probably not the wisest strategy, but it avoids external drives with their extra wires.

Daily File-by-File Backup

I used to work for a local publishing house where we used Retrospect to back up everything daily, at first to 44 MB SyQuest cartridges and later to different types of tape. Were I still working there, we would be backing up to high capacity drives instead, as they are random access and much more convenient that dealing with a stack of backup tapes. Retrospect would back up almost every file on each Mac’s hard drive (we skipped some caches and preference files, but nearly everything else).

One nice thing about Retrospect is that it was intelligent enough not to backup duplicate files.

Clones Plus Time Machine

Nowadays I back up my OS X 10.4 Tiger machine using the cloning strategy. My Power Mac G5 with OS X 10.5 Leopard has both a bootable clone and uses a partition of its internal backup drive for Time Machine, so it’s also making incremental backups during the work day. My Intel-based Mac mini running OS X 10.6 Snow Leopard and my MacBook with Snow Leopard and 10.9 Mavericks back up to a 3 TB external drive connected to a gigabit ethernet 802.11n AirPort Extreme Hub.

The biggest drawback to Time Machine is that it will back up the exact same file multiple times if it’s on multiple Macs, which means a lot of duplication if you have the same OS and/or apps installed on many different machines.

And Dropbox

The final component is multiple redundant backups. In addition to cloned partitions and Time Machine, I keep all of my important files in my Dropbox. They are synced to 2-4 desktop Macs and my MacBook. Best of all, if I mess up a file – say a word processing document or spreadsheet – I can go online and revert to an earlier version, much as I could find a specific daily backup in Retrospect.

Suggested Backup Plan

My recommendation is a three-fold backup system. For home or a small office: Make a clone of your hard drive every day, week, or month – whatever suits you best. Use Time Machine for automated ongoing file backup. And use Dropbox (or something similar) to backup files in the cloud and give you one more level of redundancy.

For a larger operation, consider Retrospect. If you have dozens of Macs with the same apps and OS versions installed, it can save a lot of backup space over Time Machine. And skip tape drives. Instead use high capacity SATA drives. In the long run, they’re no more expensive than a tape drive and stack of tapes – and a lot more convenient to deal with.

Your Hard Drive Strategy

There is no way to predict when your hard drive will fail. SMART can be helpful, but it doesn’t have great predictive power. Dropping your laptop can accelerate drive failure. But for the most part, its not predictable.

With an estimated MTBF (Mean Time Before Failure) of six years continuous use, you might feel safe, but your drive could be one that lasts a decade – or dies the first year. Even if that’s within the warranty period, you’ve got down time.

To be prepared, you should have at least three hard drives: One for everyday use, one to create a bootable clone, and one for incremental (Time Machine, Retrospect, etc.) backup. If the primary drive fails, swap in the bootable clone and then update it from the incremental backup drive.

My suggestion is a fast primary hard drive, probably 7200 rpm with a large buffer. It’s nice if your cloned backup drive is the same, but you could get by with a 5400 rpm drive with a smaller buffer. Just make sure the backup drive has at least as much capacity as your main drive. If you have multiple computers and an external clone drive, you can even move it between machines to clone multiple computers to a single partitioned hard drive.

Your incremental backup drive should be at least as big as all the hard drives on all the computers you’ll be backing up. At minimum, go for twice the in use capacity of each drive. Better yet, double the capacity of all your drives combined, because hard drives tend to fill over time. Do be aware that some Macs and PCs have problems with drives beyond 2 TB, so research that first.

On the Mac side, you could use an old Power Mac G5 with one or more 2 TB drives – the largest these Macs support – for Time Machine backup if it has OS X 10.5 Leopard installed (see Time Machine Can Now Backup to a Shared Hard Drive). Apple’s AirPort Extreme Hubs can also be used with an external USB hard drive for Time Machine backup.

Hard Drives Die

Hard drives fail, some sooner than others. The key is to be prepared. Have a bootable backup that’s fairly up to date. Have incremental backups to catch changes since then. Use a service like Dropbox to backup important files to the cloud – and duplicate them on multiple computers, even ones with different operating systems. (Dropbox support Mac OS X, Linux, and Windows.)

Don’t take a chance with your precious digital photos, your videos, your music collection, your research, your spreadsheets, your tax files, etc. Backup. Backup. Backup.

Images © 2013 by Backblaze.

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