Given the question, whether backup should be done to disk or to tape, my answer is always the same: both.
Each of these storage types has its benefits and its disadvantages and only when they are combined, you can tap the full potential of them.
As explained in my post Hardware – Tapes the essential „disadvantage“ of tape is their extremely high performance , which ist he reason, why it is (nearly) impossible to deliver the data fast enough to keep the devices in streaming mode.
Besides their price the essential benefit of tapes is the fact, that they can be easily taken out of the device and stored in a separate, secure place.
Irrespective oft he company’s interests, many management consultants still see magnetic tapes as the most reliable type of storage to back up business data to.
Today, in most cases, magnetic tapes are used as tertiary storage or 3rd level storage, whereas hard drives are commonly used as so-called nearline to or secondary storage. Because hard drives do always spin with the same speed, whether there’s data written on them or not, they qualify to serve as the primary location to put the data to, that is collected from the different servers over the network or the SAN.
In addition to this, hard drives have another benefit over magnetic tapes when it comes to restore: Since disks have nearly no search time but can address any block written on them within milliseconds, the annoying need to wind the tape to search for the needed block is not needed.
One oft he disadvantages of hard drives lies in the fact, that they are not built to be transported regularly. Therefore it is not possible to bring hard drives offsite, as it can be done with tapes.
I know, that you’ll now tell me, that there are USB disk drives that can of course be brought offsite easily. I know this. Nevertheless I don’t agree that USB drives are a serious alternative to magnetic tapes.
On the one hand, they are quite more expensive than magnetic tapes, on the other hand, they are much more sensitive to mechanical damage. Just imagine what happens, when you stumble on the stairway to the cellar where the safe for you backup media is located and drop the backup media.
A magnetic tape will survive the drop most likely, whereas the possibility of a demolition of the data stored on a USB disk drive is much higher.
And as you know, this case will always happen, if this disk contains the only usable backup of your data…
But, as I already mentioned, you can use both technologies in combination to tap the full potential of both without having to handle with their disadvantages.
Use tape drives as a secondary storage, where you target your backups to. Whether you use classical backup to disk here or deduplication, doesn’t matter.
Did your data arrive on the hard drives of your backup server, you can duplicate them to tape and remove the tapes afterwards, to store them in a secure place.
In this example, you can use the disk storage of your backup server in case you need to restore files that have been deleted or accidentally changed and use the magnetic tapes only in case of a disaster restore or when the files needed for the restore are no longer present on the disk storage of the backup server.