How do you calculate parallel availability in N + 1 and N + M systems?
should be calculated on the basis of what matters to users -- application availability. Do users care more if a particular server is up or if their database is running? Since they care about their applications, that is what you calculate availability statistics against.
If a particular server is down for 24 hours out of a week, but the critical application that runs on it had failed over to another system with just two minutes of downtime (during the failover), how would you calculate the downtime? It's two minutes out of the week, not 24 hours.
is simply the percentage of the time that the application is available out of all required time.
Hope this helps.
Evan L. Marcus
Evan L. Marcus
Editor's note: Do you agree with this expert's response? If you have more to share, post it in one of our
Dig Deeper on Data storage strategy
Storage expert Evan Marcus compares software and hardware RAID and outlines the benefits and drawbacks of each.continue reading
This expert answer explains the purpose of creating LUNs and details reasons for creating multiple LUNs.continue reading
This advice details the hardware and software requirements for setting up two data servers in fail-safe cluster mode for high availability.continue reading
Have a question for an expert?
Please add a title for your question
Get answers from a TechTarget expert on whatever's puzzling you.