Several vendors offer highly distributed storage designed to deliver very high levels of security, redundancy, availability and scalability at lower price points than RAID. For example, NEC Corp.'s Hydrastor distributes data among servers that act as accelerator nodes or storage nodes, allowing users to independently scale the amount of storage or the processing power devoted to managing it.

NEC claims Hydrastor is more scalable than clustered storage systems, "which have a finite number of controllers and storage capacity, as well as centralized file-system information and mapping tables on each node. Together, these factors create hard upper limits to scalability, forcing end users to deploy and manage additional systems that function as isolated data silos," writes an NEC spokesperson in an email.

According to NEC, the storage nodes in Hydrastor behave as a single, self-managed pool of storage that automatically balances capacity and performance across nodes, and rebalances storage among nodes as capacity is added or a node fails. In addition to lowering management costs, claims NEC, this gives Hydrastor "near limitless" scalability.

StorageIO Group's Schulz challenges NEC's claims of differentiation. "Hydrastor is a cluster as much as it is a grid, just like many other cluster-based systems are also grids," he says. He also disagrees that a grid is more scalable than a cluster, saying "it comes down to the architecture and the implementation in question and, more importantly, what is practical in terms of real-world supportable and shippable solutions vs. theoretical marketing."

Dispersed storage software from startup Cleversafe Inc. distributes data on multiple remote servers...

Gladwin says NEC's entry into the market validates the idea of clustered or grid storage. "The real competition that both NEC and Cleversafe have is the old way of doing things," he says. No matter how it's done, clustering and grid storage are the new ways of doing things, and it's up to storage administrators to choose their approaches carefully (see "Eight questions to ask a clustered storage vendor," below).

Eight questions to ask a clustered storage vendor

1. Will the vendor design an optimal file structure to take advantage of predictive caching or other features of their system?



2. What protocols do the clustered systems run? Can they take advantage of newer, lower cost protocols such as iSCSI?



3. Does the product require agents, adapters, initiators, drivers or other software to run on the application servers? These can add complexity or possibly hurt performance.



4. Is the product designed to deliver good sequential performance for streaming video or random I/O for transaction processing?



5. How many nodes will the cluster support without sacrificing ease of management and performance?



6. If additional hardware nodes are added, does the vendor charge more for clustering software?



7. If a node fails, how does the system handle data migration or replication to ensure uninterrupted application and data availability?



8. How easy is it to add new resources to the cluster?

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