Implementing BEA Portal 92

Designing Your Portal

All my examples will be based on the premise that business wants a design that can yield 99.9 percent application availability for an enterprise level of support.Many people discuss availability and say different comments: "I want it available 24-7," "It can never go down," or, my favorite, "It can never go down between 8:00 A.M. and 6:30 P.M.". We are engineers, and we deal with numbers. I've included a handy table to put hard numbers on different levels of availability. As far as keeping it up between 8:00 A.M. and 6:30 P.M., you need High Availability (HA) in your design just the same.

Note

Table 1. Availability table

Percentage Available		98%	99%	99.90%	99.99%	99.999%
Minutes/Day	1440	28.8	14.4	1.44	0.144	0.0144
Minutes/Month	43200	864	432	43.2	4.32	0.432
Minutes/Year	525600	10512	5256	525.6	52.56	5.256
Hours / Day	24	0.48	0.24	0.024	0.0024
Hours / Month	720	14.4	7.2	0.72	0.072
Hours / Year	8760	175.2	87.6	8.76	0.876

According to this table, our design will allow for approximately 44 minutes of unscheduled downtime a month. That's an important point as you craft your SLA with the business and you set your customers' expectations. What design guarantees that delivery of service? A lot depends on your experience and the state of the technology, but you cannot deliver anything more than 98 percent without redundancy on all levels. Also important to note is that you want to design your environment to allow for the availability required as well as allow for growth over a reasonable life for ...