It is no secret that disk is becoming the preferred media to use as a backup target and disk-based backup appliances are popping up all over. But as companies ready their environment for disk, a fundamental decision they need to make is selecting an appliance that presents the appropriate interface to their backup software.

Backup appliances provide either a networked-attached storage (NAS) or virtual tape library (VTL) interfaces to backup software. NAS-based backup appliances are generally easier for corporate IT staff to manage because they are configured as file servers. Since IT staff is accustomed to managing file servers, these appliances minimize learning curves and setup times.

However, a couple of downsides lurk with using NAS-based backup appliances. File systems can fill up and backup software cannot always handle these out-of-space conditions which can result in "hung" or failed backup jobs. Another possible concern is that since NAS-based backup are attached to corporate LANs, all backup traffic stays on the LAN. This can congest the LAN and put too much overhead on SAN-attached servers.

In these circumstances, VTLs may be a better option. Backup software products know how to manage out-of-space conditions on physical tape libraries so it uses that knowledge to manage similar conditions on VTLs. Further, VTLs use a block-based interface so companies can attach VTLs to their corporate SANs that keeps backup traffic off of LANs while reducing server overhead.

Companies are presented a range of options from deduplication to replication when purchasing backup appliances. But there are fundamentals that companies should focus on first and selecting a backup appliance with the right interface is one of those basics. Because while deduplication ratios and offsite replication are exciting, do not forget why you wanted disk to begin with - to ensure successful backups in shorter times.

Jerome Wendt is the president and lead analyst at DCIG Inc. You may read his blogs at www.dciginc.com