Backblaze on Data Reliability/Durability with Its Cloud Storage Service

Backblaze recently published an in-depth look at how durable/reliable data that is stored with its service is–i.e., what are the odds that you’ll want to retrieve a specific set of data from the service and find out that won’t be able to?

At the end of the day, the technical answer is “11 nines.” That’s 99.999999999%. Conceptually, if you store 1 million objects in B2 for 10 million years, you would expect to lose 1 file. There’s a higher likelihood of an asteroid destroying Earth within a million years, but that is something we’ll get to at the end of the post.

. . .

When you send us a file or object, it is actually broken up into 20 pieces (“shards”). The shards overlap so that the original file can be reconstructed from any combination of any 17 of the original 20 pieces. We then store those pieces on different drives that sit in different physical places (we call those 20 drives a “tome”) to minimize the possibility of data loss. When one drive fails, we have processes in place to “rebuild” the data for that drive. So, to lose a file, we have to have four drives fail before we had a chance to rebuild the first one.



The analysis then goes on to present a lot of math related to the time it takes for Backblaze to rebuild any data lost and its overall drive failure rate, but the general thrust is that it is extremely unlikely that Backblaze would ever suffer data loss from normal technical failures.

But at some point, we all start sounding like the guitar player for Spinal Tap. Yes, our nines go to 11. Where is that point? That’s open for debate. But somewhere around the 8th nine we start moving from practical to purely academic. Why? Because at these probability levels, it’s far more likely that:

  • An armed conflict takes out data center(s).
  • Earthquakes / floods / pests / or other events known as “Acts of God” destroy multiple data centers.
  • There’s a prolonged billing problem and your account data is deleted.

There is one thing of interest in the odd way Backblaze concludes its analysis, however,

Eleven years in and counting, with over 600 petabytes of data stored from customers across 160 countries, and well over 30 billion files restored, we confidently state that our system has scaled successfully and is reliable. The numbers bear it out and the experiences of our customers prove it.

Note that this doesn’t say that they’ve never come across a file they were unable to restore due to technical, backend reasons (rather than issues related to customer credit cards, etc.)

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