Posted by: David Boyd
backup, data deduplication, disk, tape
With the reduction in the per terabyte cost of disk and the advance of data deduplication technologies there has been an increase in speculation about what the future holds for linear tape.
Historically, and perhaps stereotypically, tape has been seen as a cheaper alternative to disk; it consumes no power when not in use and it is easily moved to an offsite location. Disk, on the other hand, has often been considered as more expensive although it requires less administration, is unaffected by slow or small data streams and has much improved restore times, particularly when restoring individual files.
Technological advancement, however, means that we should challenge these long held beliefs. Perhaps the biggest change to backup strategies has come with widespread adoption of data deduplication. Few backup vendors recommend (or support) deduplication to tape, so deduplication remains predominantly a disk technology.
Tape has long been held as the storage medium with the densest footprint, but data deduplication is changing that. For example, take a medium-sized tape library with, say, 600 LTO4 tapes each holding 1.2 TB. You’d expect this library to consume the majority of a rack. But, if this data is deduplicated at a ratio of 20:1 the library could be replaced by just a couple of disk shelves. Since space has become as precious to data centre managers as power and cooling capacity the potential savings of moving from tape to high capacity deduplicated disk cannot be ignored.
One key advantage of tape is the ability to move data to a remote location easily, but again data deduplication is allowing organisations to work smarter. Historically, in all but the largest companies the cost involved in acquiring network infrastructure to allow you to replicate large volumes of backup data between physically remote sites has been prohibitively high.
Now, because optimised deduplication only replicates unique data chunks between storage devices, smaller organisations that could not previously afford it can copy backup data between sites over low bandwidth networks or networks with high latencies.
Indeed, as WAN performance increases and data deduplication technologies mature, smaller organisations may look to send backup data to the cloud, although the fear of long recovery times will still deter many IT managers.
Long term retention of data is a cornerstone of many organisations’ compliance policy and while many studies show disk can be cheaper than tape for short- to medium-term retentions, backup data that requires long term retention (a year upwards) is still far better placed on tape. Over these longer durations tape consumes less power, doesn’t incur an ongoing maintenance cost, and the data stored on it is less likely to become corrupt.
Disk is becoming increasingly attractive as a replacement for tape in the backup arena and some of the long held advantages that tape has had over disk are being challenged. However, tape still has a place in the data centre. Backups with long retention periods and archived data are still based placed on tape and this is unlikely to change. Indeed, the roadmaps provided by tape and tape library vendors suggest that the future of tape in large organisations remains strong – technology investments of this scale would not be happening if tape was doomed.