[olov]

"If the price were right, we would be buying nothing but Hitachi drives."

I don't understand why they don't. Are the Hitachi drives really that much more expensive so that it doesn't justify their vastly longer lifespan? Even if they can get "free" replacement disks during the warranty period, that has a cost for them. And they mentioned that some replacement disks die even faster.

I'm sure Backblaze has crunched all these numbers - would love to see them. BTW thanks for sharing this data!

[rtkwe]

Looking at PCPartPicker (no drive shucking) Hitachi drives are at least $.02 more per GB than similar (7200RPM >= 1TB) WD and Seagate drives. Which means a difference of ~$20 per TB of storage, which at 1 pod (180TB) every few weeks means they're saving something on the order of 3.5k every few weeks using the cheaper drives. How much the additional failure rate costs them would be wild speculation, between RMAs/warranties and labor there are lots of assumptions to make, so I'll stop there.

eg:

    Hitachi 0F10311	Deskstar 7K2000 (7200RPM) : $0.059/GB

    Western Digital WD30EFRX RED (5400RPM) : $.044/GB

    Seagate ST3000DM001	(7200RPM) : $.034/GB

http://pcpartpicker.com/parts/internal-hard-drive/#m=19,34,3...

[brianwski]

Backblaze employee here - it is honestly just a spreadsheet that kicks out the answer. Every month we ask 20 or so suppliers for the lowest price for each drive type. If Hitachi are 10 percent more expensive but fail 10 percent less often, that balances out and we buy Hitachi. But if it is 12 percent more costly then we get the other brand. There is a tiny bit of free preference leeway given to Hitachi because it means less hassle to our over worked datacenter team...

[olov]

If I'm not reading it wrong then your data says that the Hitachi drives have half the Annual Failure Rate, or less, than the others (in your setup). Not sure what this means in MTBF but the Hitachi's sure seem to be worth a whole lot more, certainly 10, 20 or 30 percent more - no?

[brianwski]

I don't think the math works. I posted this above:

I think the calculation is replacing one drive takes about 15 minutes of work. If we have 30,000 drives and 2 percent fail, it takes 150 hours to replace those. In other words, one employee for one month of 8 hour days. Getting the failure rate down to 1 percent means you save 2 weeks of employee salary - maybe $5,000 total? The 30,000 drives costs you $4 million, so who cares about $5k here or there?

The $5k/$4million means the Hitachis are worth 1/10th of 1 percent higher cost to us. ACTUALLY we pay even more than that for them, but not more than a few dollars per drive (maybe 2 or 3 percent more).

Moral of the story: design for failure and buy the cheapest components you can. :-)

[olov]

Ok, after converting to MTBF the numbers make more sense: An AFR of 0.9% means a MTBF of 968947 hours (111 years). An AFR of 3.2% means a MTBF of 269346 hours (31 years).

I guess an MTBF of 31 years is plenty for your needs. Thanks again for sharing the data.

[im3w1l]

I think the failure rate will go up in old age. I just don't see those drives still working in 100 years.

[joeframbach]

The cost you see on newegg probably isn't the cost Blackblaze sees. They're getting bulk pricing, which WD is probably more eager to sell than Hitachi.

[brianwski]

No, we are not getting bulk pricing. At least not really by much. We sometimes still "farm" where employees all visit Costco to buy drives RETAIL, we also buy from Amazon and NewEgg. Honestly, we just cannot seem to get good deals on drives! If anybody on earth can get these magically better prices, we are begging them to come forward, we promise to give you 99 percent of the cost savings. Beat our current suppliers by 1 penny per drive and you take all our business. We're buying about 800 drives per month, shut up and take our money! (Each drive is 4 TBytes)