With your SLA in hand, take inventory of the server, networks, storage, people, and other resources at your disposal. Now is the time to estimate whether it is possible to meet the requirements at all.
If for example you are expected to serve more throughput than the network can transfer, maintain high availability with only one physical machine, store 100 GB of backups on a 50 GB partition, or provide 24/7 support all alone, no amount of tweaking available resources is likely to fix the problem.
When checking that the resources you have at least theoretically suffice to meet your requirements, do not forget that high availability in particular requires at least two of everything to avoid single points of failure. Be sure to list the resources you expect to have, when and how long you expect to have them, and why you need them. Also make note of what is missing and why.
