Cross-Platform Company Storage Architecture?

Eric^2 asks: "My company is preparing to implement a major network storage upgrade, and I'd like to get some ideas from Slashdot about what devices should be considered, and hopefully some experiences with some of the offerings that are available. What types of storage are you using and what would you recommend?" "We are currently using approximately 2TB of storage space, and will need to expand to over 10TB in the next two to three years. We have a mix of Windows, Mac OS X, and Linux clients and servers. All of our authentication is presently done through an Active Directory. If possible, we would like to centralize all of the storage into a single namespace, such as OpenAFS or DFS. Anything we purchase will have to be under maintenance contract for hardware such as failed drives or controllers. Ideally, whatever system we choose would allow us to purchase both high-speed SCSI spindles for our transactional needs and lower-speed SATA high capacity drives for our archival storage needs."