Blog

There seems to be a lot of confusion around disk-based backup and VTL. Many use these words interchangeably as to imply that disk-based back up is VTL and VTL is disk-based backup. The truth is that VTL is an interface between the backup server and the disk.

All backup applications can  write to three targets:

1. Tape library
2. NAS shares (network attached storage device share)
3. Disk volume - any disk

If you want to backup to disk you have 3 choices:

1. If you want to write in tape mode then you need to put VTL between the backup server and the disk. The VTL emulates a tape library on the front end and writes to disk on the back end. Up until a few years ago this was the only way you could write to disk. But then the backup applications all added the ability to write natively to disk by adding the ability to write to a NAS share or disk volume. Therefore, VTL has gone away in the mass market as it was a stop gap. However, it still has value in Fibre SAN environments.
2. You can point back up jobs at NAS shares. Simply plug a NAS server behind your backup server and point your backups at NAS shares.
3. You can point backup jobs at disk volumes. This is the least common method in the industry...as all the products with data de-duplication use either NAS or VTL.

The industry is dividing into two camps as the disk-based backup systems with data de-duplication in the market offer either NAS or VTL.

1. If your backup server is on a Fibre SAN and you want the disk-based backup product on the Fibre SAN, VTL can handle SAN block level traffic. This tends to be the case mostly in the large enterprises.
2. For the mass market of mid market to small enterprise customers where they don't have a Fibre SAN--or if they do have a Fibre SAN, their backup application is on the Ethernet network and not Fibre, then the solution of choice is to connect a NAS based disk-based backup system. NAS is connected via Ethernet to the disk-based backup system. This can be over the Ethernet network or to keep the traffic off the Ethernet network this can be a private Ethernet connection between the backup server and the disk-based backup system.

Bill Andrews is President and CEO of ExaGrid Systems a company that provides fast, low cost and scalable disk-based backup with data de-duplication solutions.