Your organization is updating runbook documentation for a new ERP server cluster. Management specifies an uptime requirement of 99.95%, measured over each 30-day month. When writing the maintenance-window section of the document, what is the maximum total downtime you can schedule per month without violating the requirement?
About 43 minutes 12 seconds of downtime per month
About 4 hours 23 minutes of downtime per month
About 7 hours 12 minutes of downtime per month
About 22 minutes (21 minutes 36 seconds) of downtime per month
Uptime percentages define how much downtime is permitted in a given period. For a 30-day month (43,200 minutes), 99.95% availability allows only 0.05% downtime:
Documenting a maintenance window larger than this would exceed the stated requirement. The other figures correspond to different availability targets: roughly 4 hours 23 minutes is the annual allowance for 99.95%; 43 minutes 12 seconds is the monthly allowance for 99.9%; and 7 hours 12 minutes is the monthly allowance for 99%. Therefore, scheduling no more than about 22 minutes of downtime per month is the only choice that meets the 99.95% uptime requirement.