This piece, discussing the benefits of moving to an all disk backup solution, caught my eye. It struck me because I think the author is just right—there are a lot of good reasons to be moving from Disk to Disk to Tape (where tape is used for offsite) to Disk to Disk to Disk. Reliability, durability, recoverability, and so on all favour disk as an off-site target. I think the author is also picking up on an important secular trend that is largely inevitable at this point: disk as the only target for backup and recovery system.
But there is another important reason to move to all disk: cost. I will have more to say about the TCO of disk backup solutions shortly, but one of the most striking, and perhaps counterintuitive things about D2D2D is that it usually has a better Return On Investment (ROI) and a relatively lower TCO than D2D2T. That is to say: using disk for off-site rather than tape is usually easier to cost justify than using disk for onsite.