Choosing a primary storage solution for your organization can be a complicated task. Perhaps the most important thing you can do to ensure that you end up with a well-designed and cost-effective solution is to have a solid understanding of the storage needs of your environment -- both present and future. If you fail to do this before you start to review the myriad storage solutions on the market today, you'll waste a lot of time and may end up with a solution that doesn't fit your needs.
Unless you are intentionally buying storage that will be dedicated to a single high-performance system, the best place to start is to look at literally every storage user in your environment. Highly redundant, high-performance primary storage is not cheap. So the best way to leverage the investment you're going to make is to ensure that it delivers the maximum benefit to largest percentage of your infrastructure as possible.
Here are some quick rules to follow and common pitfalls to avoid in the key areas of consideration.
Your current storage capacity requirements are probably the easiest thing to determine. Look at the disk space used by all of your servers, add that up, and voilà -- you have a number. But of course, it's not that simple. There are three core factors to consider that can cause your storage estimate to be inaccurate.