There has been a drop in the price of disk storage that has led to many organizations adding disk as their backup mechanism, which I believe is just psychological with respect to modernization – disks seem more modern than tapes like the evolution of cassette tapes for music to CDs. However as through time’s test, tapes have kept their competitive edge with respect to long term storage.
As for performance tape drives have evolved to become very fast, some capable of writing at 280 MBps – a figure that outperforms disk – particularly the cheaper disks normally chosen for backup. However, the infrastructure you have should support tape as the medium really suffers in less than optimum conditions.
When it comes to a restore needed, the seek time on a disk can be a matter of a few milliseconds whereas a tape can take longer and you may end up having to locate the correct physical tape then loading it into a drive.
Touching on manageability, tapes portability is its obvious advantage. They can be restored offsite, protecting them from system wide disruptions. Disks do not have that flexibility though strong networking makes transfer of data to your remote site a breeze, providing the same benefit.
