> I wonder if [Netflix is] space limited or iops limited.
I don't think you're asking the right question. The more iops, the less space and the less cost. I'd say Netflix is always optimizing for both.
The right question to ask is what is the break-even point between space and cost where these drives make sense, and that would depend mostly on how popular the most popular content is. If everyone were watching the same few things, but enough that it can't just all fit in RAM, it would make a lot of sense to have a lot of these drives. But if the watching is spread out across a lot of content, then not so much.
According to instantwatcher.com, there are 6843 movies on Netflix streaming currently. If we conservatively say that the 1080p stream is 2gb, and the other formats add up to another 2gb, that's a total of ~27 TB of space required.
There are 3657 seasons of TV, let's say an average of 2gb per episode, and an average of 14 episodes a season. That's ~102 TB.
So napkin math suggests ~129TB of storage to hold all of Netflix, or 33 of these drives.
Since they need redundancy and to have servers distributed around the country for peering, and these drives will probably cost ~$10k each (5x premium on consumer), I doubt they'll be putting their long tail content on them.
How many people in Boston are currently watching Mission Impossible, the TV series from 1966? Or content like it? A standard hard drive can serve 500 people HD streams so long as you cache ahead into memory intelligently in big enough chunks.
Within a few generations, SSDs will probably be cheap enough to not even bother with mechanical, for this and many other use cases.
Hmm.. I read that a 2 hour Netflix movie is about 2 GB. So you need ~2.2 Mbps per user or 183 iops / client in terms of 1.5K packets.
One drive can fit 2000 movies. 75K iops/drive / 183 iops/client = 400 clients/drive (this is 900 Mbps, but the drive says up to 400 MB/s, so not bandwidth limited).
Put 16 in a 2U server for 6400 clients. This is 14 Gbps, so you need two 10 G NICs to complete our Netflix appliance.
But you are right, if caching works we don't need all these drives. With 128 GB of RAM we can fit 64 movies in RAM. I could easily believe that most people only watch the popular movies.
I don't think you're asking the right question. The more iops, the less space and the less cost. I'd say Netflix is always optimizing for both.
The right question to ask is what is the break-even point between space and cost where these drives make sense, and that would depend mostly on how popular the most popular content is. If everyone were watching the same few things, but enough that it can't just all fit in RAM, it would make a lot of sense to have a lot of these drives. But if the watching is spread out across a lot of content, then not so much.