Computer Hard Drives

Failure Rates, Prices, Backup, and More

What's a Hard Drive

Wikipedia says “A hard disk drive (HDD)is a data storage device used for storing and retrieving digital information using rapidly rotating disks (platters) coated with magnetic material.”  Basically, it’s the device upon which most computers store all those photos, music, and movies that we keep.

Many laptops now use a different form of storing data called SSDs, which store data on flash memory, without any rotating disks. This hard drive resource article only deals with disk drives, not SSDs.

Hard Drive History

The first hard drive was produced in 1956 by IBM. That disk drive was the size of a car, stored a mere 3.75 megabytes, and cost $300,000 in today’s dollars.

A typical hard drive today is about 2 cubic inches, stores 4 terabytes (4,194,304 megabytes) and costs about $150.

From it’s inception in 1956 the hard drive has decreased in size 57,000 times, increased storage 1 million times, and decreased cost 2,000 times. In other words, the cost per gigabyte has decreased by 2 billion times in about 60 years!

Hard Drive Reliability

Hard disk drives are incredible feats of engineering. Imagine a record spinning 10 times per second, with nothing but the width of a DNA-strand between the record and the needle, simultaneously playing music and writing new music to the record. Now consider all of that precision going on in the less than optimal conditions the real world presents. For example being tossed onto a table at a cafe, for years, without issue. Pretty impressive.

Having said that, hard drives do fail, and different drives fail at different rates. Hard drive companies use one of two reliability metrics:
  • Mean Time Between Failure (MTBF)
  • Annual Failure Rate (AFR)
Seagate has transitioned away from MTBF (previously reporting between 300,000 and 1,200,000 hours of operation) to AFR (which says, for example, that for one of their drives to expect 0.73% of them to fail annually.)
In practice, some drives are dead-on-arrival, while others last for many years.

Backblaze runs a cloud storage system with over 100,000,000 GB of customer data stored on over approximately 40,000 hard drives.

High-Level Summary

With 40,000 hard drives, Backblaze knows a lot about the reliability of hard drives and shares the statistics:
  • 78% of drives survive more than 4 years.
  • The median hard drive survives 6 years.
  • Drives have 3 distinct failure modes that follow a bathtub curve:
    • Early “Infant Mortality” Failure
    • Constant (Random) Failure
    • Wear Out Failure
  • As long as the temperature is within spec, reliability is not affected by heat.
  • HGST drives are generally reliable; Seagate and Western Digital hard drives’ reliability vary by model.
Additional Resources

Hard Drive Pricing

While price per GB has decreased by 2 billion times, the amount of data we store has dramatically increased and we expect our hard drives to be cost efficient.

With over 40,000 hard drives Backblaze needs to track drive pricing carefully. Here is a graph of the cost per GB for hard drives from approximately 2008 - 2013.
The results of 'Hard Drive Farming' from store shelves.

Hard Drive Farming

In October 2011, Thailand had the worst flood in 50 years. What does that have to do with hard drives? Half of the world’s hard drives were manufactured in Thailand. Along with loss of life and property, the flood destroyed hard drive factories.

The result of this was that hard drive supplies dried up, making it incredibly difficult to buy hard drives, and the prices doubled and tripled. Many companies that were dependent on hard drives raised prices on customers to support the increased cost of drives.

In order to make it through this time without raising prices on customers, Backblaze started “hard drive farming”. The company needed about 1,000 “internal” hard drives per month to install in servers. However, since “internal” hard drives were unavailable, the company tried cracking open “external” hard drives that would normally be used by individuals to plug into their computers via USB. Finding the actual hard drives were the same, they started a process of trying to acquire 1,000 of these “external” hard drives by driving to every retail store in the area. With employees, family, friends, and customers involved, drive farming was in full effect. Read more about the craziness that this entailed:
Farming hard drives: how Backblaze weathered the Thailand drive crisis

Hard Drive Backup

A single 4 TB hard drive can store 500 full length movies, 250,000 irreplaceable family photos, 250,000 curated songs, and still have enough space for over a million documents, spreadsheets, and other small files. That’s a lot of data to lose to a single drive crash.

There are various ways to backup a hard drive, but the two most common are:

  • Backup to another hard drive: this is reasonably easy to do once since you can just copy all the data over. However, it is hard to keep the backup hard drive up-to-date with changes. Also chances are you’re keeping both drives close together, which means they can both be destroyed by a single event.
  • Backup to the cloud: Cloud backup (or “online backup”) can automatically backup the data from the hard drive over the Internet to a remote location. This makes sure you don’t have to remember to do the backups and keeps the data safe from localized risks.
Backblaze is a leading cloud backup service that:
  • Automatically backs up all data from your hard drives
  • Keeps all the data securely encrypted
  • Provides you access via a web browser and iPhone & Android apps
  • Enables recovery via a FedEx’ed hard drive or flash drive
  • And costs just $5 per month per computer for unlimited data & unlimited hard drives