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 4 hours 23 minutes of downtime per month
About 7 hours 12 minutes of downtime per month
About 43 minutes 12 seconds 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.