NAS (network-attached storage) appliances have long been popular in small and midsize businesses and are now plug-and-play simple. But adding a second and third NAS means you need to add second and third volumes and management consoles. To eliminate the hassles of juggling storage across separate repositories with redundant management, vendors are introducing scale-out NAS appliances at SMB-friendly prices.
As usual, the definition varies from vendor to vendor. George Crump, president and founder of analyst firm Storage Switzerland, defines scale-out NAS as "nodal in nature, with some sort of data striping across those nodes." In other words, one interface for an expandable storage cluster.
The "why" is simple, according to George Symons, CEO of Gridstore Inc., a maker of scale-out NAS products in Mountain View, Calif. "You want to have a file system interface, CIFS or NFS, able to incrementally add capacity while keeping performance going." Traditional NAS products let you add extra drives, but not without shutting down the system and rebuilding a RAID file system to provide redundancy. Scale-out NAS systems make adding capacity faster and easier.
Used in enterprise systems, scale-out NAS appliances are moving into the medium business market, and some are beginning to filter down to small businesses. To maintain performance, most scale-out NAS appliances add their processing power to the cluster of other scale-out NAS units already in place. This increases expense for each appliance, and requires software to coordinate storage management across the cluster.
Gridstore took a different approach, says Symons. "We rely on the intelligence in the server and steal a few CPU cycles to keep our cost very attractive." Gridstore's approach doesn't use RAID, but the company's own fault tolerance and redundancy schemes. This allows Gridstore to avoid the expense of RAID engines and dual controllers. Since the server or client manages the storage, performance doesn't drop as more nodes are added to the storage cluster, as can sometimes happen with other scale-out NAS appliances. On the other hand, Gridstore requires changes to all servers and clients accessing that pool of storage.
Another new entrant in the scale-out NAS market, Sunnyvale, Calif.-based Exablox, uses its own object-oriented file system and was advised by James Gosling (Java) and Ken Thompson (Unix and C). Any two drives in an appliance can fail without damaging data, and the same is true of any two appliances in a cluster. No RAID, no LUNs (logical unit numbers), no volumes, says Exablox CEO Doug Brockett.
The market for scale-out NAS appliances will continue to grow, says Crump. "As more SMBs start using NAS for virtualized servers, the capacity and bandwidth and performance demands on networks and storage processors will keep going up." Scaling out the processing power, as well as storage capacity, will help those doing thin provisioning, replication, and virtual machine snapshots.