The number of hours a group of drives are in operation over the period of observation.

The number of drive failures in the defined group over the period of observation.

A period of observation, typically a year.

A defined group to observe, in our case a group of drives, usually by model.

There are two different ways to do this, either works.įor the first way, there are four things required: This is a good point to review how we compute our drive failure rates. Note that drives retired and removed from service are not marked as “failed,” they just stop accumulating drive-hours when they are removed. The cumulative failure rate is based on data from Q2 2013 through the date when the last drive was removed from service. The drive count is the number of drives reporting as operational on 31 December 2015.ĭuring 2015, five drive models were retired and removed from service.

The failure rates and confidence intervals are cumulative from Q2 2013 through Q4 2015. These are the hard drives used in our Storage Pods to store customer data.

The table below contains the statistics for the 18 different models of hard drives in our data center as of 31 December 2015. Let’s start with the current state of the hard drives in our data center as of the end of 2015 and then dig into the rest later on. Not only was 2015 a year of growth, it was also a year of drive upgrades and replacements. We added 65PB of storage in 2015, give or take a petabyte or two. By comparison, 2015 began with 39,690 drives running in 882 Storage Pods. These hard drives reside in 1,249 Backblaze Storage Pods. For the most recent hard drive reliability statistics, as well as the raw hard drive test data, visit Hard Drive Data and Stats.īy the end of 2015, the Backblaze data center had 56,224 spinning hard drives containing customer data.

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