Backblaze unabashedly sources the cheapest consumer drives they can find for storing their customers' data. Their noble goal is to provide storage as cheaply as possible, and then pass those savings along to their customers. They do not use drives indiscriminately, each model goes through a short test phase to assure the drive suits their purposes. Pairing these cheap drives with various RAID and replication schemes provides enough integrity to safely store data.
During the Thailand flooding in October 2011, Backblaze had to go to extreme lengths to procure enough drives to sustain operations. With the prices of HDD's rising exponentially, and supply in short stock, they literally took to the streets as a drastic form of damage control. They named the practice 'drive farming'.
First, they found that buying external drives was very cost effective. The whims of the market dictate that external drives are often cheaper than internal desktop drives. These drives come in small enclosures and are usually connected via USB or eSATA. Backblaze buys these drives, and strips the drives from the enclosures in a process they lovingly refer to as "shucking". Much like shucking a head of corn, they rip the enclosure apart and out pops a useable HDD.
At first they pillaged area Fry's and Costco's until some employees were eventually banned from purchasing more drives. They fanned out further and enlisted the help of friends and family to continue purchasing drives, even detailing complex drive purchasing schedules to skirt drive purchasing limitations. When this approach began to fizzle in the local area, they even pondered going cross-country in Ryder truck. This eventually led to crowdsourcing. Backblaze offered their readers a $5 bounty per drive for drives purchased and sent to them during a Costco sale.
This practice exhibits amazing ingenuity and a laudable effort to deliver the best bang for the buck to their customers. Unfortunately, it doesn't mesh well with creating a stable sample pool to determine drive reliability. Backblaze also acknowledges using drives that were known RMA's, and refurbished, in the sample pool.
The majority of Backblaze's failures occur in the first few weeks of service, which is understandable considering their drive purchasing methods. The typical 'bathtub curve' of failures is expected with many storage devices, with the highest chance of failure in the beginning and ending stages of the product's life. However, it is feasible to conclude that their drive sourcing methods tainted their results.
Interestingly enough, Backblaze won $5 million in venture funding. Soon after, Costco was offering a sale on external HDD's with a limit of five per person. Even with the massive funding, they chose to take advantage of the sale to get the best bang for their buck. As they stated, old habits die hard.
Unfortunately, these drives are included in their failure ratings.