Pros and Cons of Virtual Tape Libraries

Tape data storage just keeps on going. It’s almost like the steam punk of IT, a branch off into a different universe where everybody reads with bigger candles instead electric light bulbs. But it works. In fact, it works well enough for the largest IT vendors to continue pushing the envelope on data storage density on tape and storage and recovery speeds too. However, tape is not disk. You cannot ‘dip into’ tape in the same way you can randomly access a hard drive. And so, for backup and recovery in particular, the virtual tape library was invented to offer advantages of tape and disk altogether. Nevertheless, there are both pros and cons to consider.

Let’s start with the pros. Virtual tape libraries (VTLs) are made to work with backup software and processes that support tape. Disconnect your tape drives and hook up your hard disk array with its VTL technology to enjoy immediate improvements in performance over tape. Disks avoid the streaming that physical tape drives must use and write efficiently independently of data transfer speed. This makes VTLs good for older systems generating many very short tape volumes. Data restoral is typically faster too. Finally, VTLs don’t suffer from the PEOT (physical end of tape/’full’ indicator) phenomenon that leads to many tape cartridges only being reused if the user is sure that all the content can now be erased.

However, VTLs don’t do as well as tape in other respects, notably cost and isolation from danger. Tape is still king of the heap in terms of price per gigabyte stored. It can also be taken offline and off-site to protect it from power spikes, lighting or other local disasters. By comparison, VTLs sitting on disks generally stay connected and therefore more vulnerable. But there’s an answer to that too, at least in terms of enhancing security. VTL products often offer replication to another VTL or a physical tape device. Some also have the intelligence to examine incremental backups and only replicate the parts that changed. Finally, the best solution might just be the right mix of both virtual and physical tape libraries.