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Some cloud providers are talking about six or nine or even 13 nines of availability. Promoting five nines of availability is something the cloud providers are doing that I think resonates with customers because the providers are bringing the term durability into the conversation. That's something the traditional vendors aren't picking up on quite yet.
Availability equals accessibility plus durability. Accessibility is, "Can I get to the data? Can I get to the application, or not?" It also includes such aspects as reliability and resilience.
Durability refers to how many copies there are -- so, if I can get to it, are there multiple copies or versions? So, it's possible to have high durability with low accessibility. It means data is intact and there are multiple copies, but it can't be accessed for one reason or another.
On the other hand, you could have low durability, and high availability, which means I can get to the data but it's not there; something's missing. This is why you're starting to see more than five nines of availability. In the past, we've seen five nines, six nines, or the minutes of downtime per year. What this all comes back to is that when you see a higher number of nines, first ask this question: "Is that accessibility, in terms of availability, or is that durability -- the number of copies of data, or is it some combination?"
IT professionals, particularly people in the storage world, are used to thinking in terms of availability: "Is it on? Can I get to it?" They're not thinking of it as a multidimensional measurement.
If somebody says, "10 nines, 13 nines, 15 nines of availability is impossible," they're wrong, because you can achieve those numbers very easily if you put durability into the conversation, and this is what the cloud providers are doing. So, it's the sum of those parts.
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