Network Attached Storage (NAS) is increasingly popular because it's inexpensive, easy to manage, and scalable. As a network device, its use of well-known network protocols such as NFS and Common Internet File System (CIFS) make it an ideal file-serving storage device. You need minimal expertise to administer and manage NAS. Because the NAS devices' sole purpose is to provide storage to applications that need them, the NAS OS has few complexities. Total cost of ownership (TCO) for NAS is low because disk space is inexpensive and administration costs are modest.
In contrast, Storage Area Networks (SANs) offer additional data-management functionality, but SANs are also significantly more complex and require more in-depth administration. One important benefit of SANs is that they let administrators perform backups efficiently by moving the large volume of backup data from the LAN to the SAN. Moving backup traffic from the LAN to the SAN lets you utilize the LAN for application and messaging traffic, which is especially valuable in environments where data is growing significantly while backup windows are shrinking.
Data that resides on a NAS device has the same backup requirements as data residing on the SAN. Overall, NAS environments experience the same data growth and backup-window problems as other environments. Backing up NAS devices presents a problem because NAS devices are directly connected to the LAN. Efficient use of secondary storage devices such as optical jukeboxes or tape libraries requires that distributed NAS devices send their data across the LAN during backup, perpetuating the network problems already associated with traditional LAN backup.
Fortunately for the many end users who've purchased NAS for its scalability and ease of management, a group of companies has been working cooperatively on a network-based protocol—Network Data Management Protocol (NDMP)—that will let intensive data-migration activities such as backup use secondary storage and network resources more effectively. As vendors incorporate NDMP into commonly available backup products, NAS becomes an increasingly viable storage solution.
Because NAS devices are highly optimized for one function—file serving—they have little more than a general-purpose OS with a thin kernel. A NAS appliance can't host enterprise backup-server software. Even if you connect secondary-storage devices directly to the NAS device, the storage must travel over the network and through the backup server for processing, which perpetuates the poor use of the LAN for backup traffic. Any time you overload the LAN with backup traffic, a purpose for which it's not suited, the performance of the applications on the LAN suffers.
The NDMP protocol addresses this problem of backup traffic on the LAN by separating the file and backup metadata processing from the transfer of data between storage devices. The protocol specifies communication between the NDMP server (residing on the NAS device) and the backup software. The NDMP server considers each backup-software server component to be an NDMP client. To act as an NDMP server, the NAS device must be NDMP-compliant. In addition, backup software must implement the protocol in the form of an NDMP client. When the system backs up a NAS device, the NDMP server performs tasks related to backup-client authentication and management of the data and tape interfaces. The backup software initiates data movement, receives metadata information for cataloging, and performs tasks related to application-specific notification and logging.
Why is this important? The NDMP protocol lets NAS vendors work closely with data-management vendors (i.e., backup and recovery vendors) to remove one barrier to NAS adoption. Despite its benefits, NAS loses some of its allure if NAS data protection requires that burgeoning amounts of NAS storage travel the LAN for backup. NDMP lets backup vendors easily support backup of NAS devices while managing the information about the backups in the context of the entire enterprise backup scheme. NDMP lets NAS backups coexist with traditional enterprise-network backups without special programming, management, or interoperability concerns between NAS vendors and backup vendors. The NDMP protocol will help customers gain the benefits of NAS without the current drawbacks. For more information about NDMP, visit the NDMP Web site.
