Tape or Disk Backups? – Why not do Both?


Discussions about whether to go for disk or tape as a back-up medium are frequent, but there’s still no knock-out result one way or the other.


To reach any conclusion, you need to know the advantages of tape backup in disaster recovery, and how to sidestep any tape backup risks. In many instances, the pros of tape are the cons of disk, and vice versa.

Small wonder therefore that they can complement each other for a reliable, cost-effective solution. Is a balanced combination of both disk and tape then better than using either one exclusively?

Before discussing tape backup risks, let’s start with tape back-up advantages compared to disk.

First on the list is cost. For large volumes of data (think terabytes), tape still has a clear cost advantage per volume unit stored. Even though disks have made staggering progress in terms of capacity over the years, tape is still the winner.

Surprisingly, tape also wins in terms of performance concerning speed of writing data to the storage medium (careful – the speed of getting that data back is another story, see below). Thirdly, tape is easier to manage for safe storage. Just remove the cassette, take it off site or lock it away in your secure tape archive, for example.

So what are the tape backup risks? Seeing restore speeds for specific data slow to a snail’s pace is a big one. Whereas disks can boast access times as low as 10 ms by directly accessing the disk sector concerned, it can take minutes (or more if you first have to mount the tape) to fast forward a tape to find a particular piece of information. Tape simply doesn’t have the random access possibility of disk.

The solution? Here’s one candidate: store your latest backup on disk for fast restores, while copying backups in general to tape for lower-cost long-term storage and off-site removal.