From the largest multinational down to the humblest mom and pop e-business, companies are facing explosive demand for storage. E-mail. Mission-critical applications. Data retention and compliance. Digital content. Availability and data recovery. The list at times can seem endless.

The surge couldn't happen at a worse time for IT managers, many of whom are facing flat or only slightly increased budgets. Even so, data managers are allocating more of that shrinking pile of money to storage concerns. According to a recent survey by Forrester Research, 40 percent of enterprises said they plan to spend more on storage hardware in the coming year, with another 46 percent saying their spending on storage will be level.

Companies are investing in storage because they have to. Forrester estimates storage capacity requirements are growing at a rate of between 15 percent and 25 percent per year. Here are just a few of the reasons why:

An ever-increasing reliance on e-mail and instant messaging
The more companies come to view their communications systems as mission-critical applications, the more they need to service and store that data reliably. And the volumes are never-ceasing: one estimate from the Radicati Group posits that the average corporate email user sends and receives a total of 84 messages per day and that the average size of a message without an attachment is about 22 KB. By 2008, the firm estimates that an average corporate e-mail user will process up to 15.8MB of data per day. So, for a company with 1,000 users, that's an average of 10GB per day -- or 200GB per month. Ouch.

The contained growth of production data
Fueled by continued growth in business-processing applications like CRM (customer resource management) and ERP (enterprise resource planning) and a burgeoning burden of rich digital content--images, sound and video--Forrester estimates the current annual growth of production data at 20 percent to 30 percent will continue for at least the next five years.

Greater expectations for data and applications availability
In the age of round-the-clock business operations, companies that aim to stay competitive are increasingly ranking their disaster-recovery and applications availability as one of their highest priorities--a situation that most often requires state-of-the-art, highest-speed networked storage solutions.

How are companies coping with the storage upsurge? First and foremost, companies of all sizes are moving away from tape and toward disk-based data protection, with smaller companies taking a particular interest in easy-to-switch-to options like virtual tape libraries. Networked storage also is an up-and-comer, with small and mid-sized businesses attracted especially to networked-attached storage (NAS), which enables them to deliver content to storage-hungry applications in a plug-and-play manner via common Ethernet protocols.

Finally, corporations with highest-end storage needs, and the money to invest in storage infrastructure, are moving into storage area networks (SANs), of both the fast-but-pricey Fibre Channel variety, which is most popular just now, or the apparent network storage wave of the future, SAN over the ubiquitous IP protocol. Massive storage capabilities over the world's most global protocol? What's not to love.