Similarly, vendors that offer both multiprotocol arrays and SRM apps such EMC ControlCenter and Hewlett-Packard (HP) Co. Storage Essentials typically provide tighter integration and more advanced management options for their own multiprotocol arrays.

"For NetApp filers and the HP StorageWorks All-in-One Storage System, we offer a Storage Essentials agent that extends the full SRM capabilities to file-system protocols," says HP's Dean Schneider, marketing planning manager for Storage Essentials.

Array features
The features in some multiprotocol arrays are on par with, and in some cases ahead of, single-protocol arrays. Snapshot and replication have become standard features in arrays supporting NAS and SAN. While all vendors support replication, they differ in their implementation of it. Does the array support synchronous and asynchronous replication? Can replication be performed at a file and block level, or is it limited to one of the two protocols? NetApp and Pillar Data Systems, for example, support synchronous and asynchronous replication, and storage administrators have a choice of file- and volume-based replication.

Multiprotocol arrays provide a wider range of backup options than block-based arrays. Besides snapshot and replication, users can directly back up data through CIFS and NFS file-system protocols without going through another server. Moreover, the majority of multiprotocol arrays--Windows Storage Server excluded--support the Network Data Management Protocol (NDMP), which is optimized for backup and eliminates the need for installing a backup agent on the storage system. Being Windows based, the lack of NDMP support in Windows Storage Server isn't much of an issue, as most Windows Server 2003-compatible backup applications will also run on Windows Storage Server.

Thin provisioning is becoming increasingly important and is available in multiprotocol arrays from EMC, HDS and NetApp. Deduplication is another feature making inroads. While a few vendors have some level of deduplication, NetApp is currently the only multiprotocol array vendor offering a deduplication option for all of its filers.

Price
If both file- and block-based protocols are required, procuring a multiprotocol array or NAS gateway is significantly less expensive than buying two arrays. "As a rule of thumb, you can add about 10% of the array price for additional protocols," says NetApp's Bennett.

In general, arrays from leading storage vendors like NetApp and EMC include only a limited number of features in the base price, and extra features and protocols have to be bought separately. Some customers are repelled by having to pay for features they expected to be part of the base price and are driven to array vendors with a more inclusive pricing model.