SAN concept turned on head by vendor

One pool of storage from many servers claimed

French start-up Seanodes has a product that combines storage on many Linux servers into a single shared pool of storage, making networked storage unnecessary.

The Exanodes software runs on each Linux server and adds its unused direct-attached storage (DAS) into a Shared Internal Storage (SIS) pool which acts, in analyst firm IDC's words, as an inside-out SAN. This is viewed by applications as a traditional external shared array and can be either implemented alone or as a complement to existing external storage (SAN or NAS).

The individual servers are clustered together and the nodes can act both as application and storage servers. A 32-node Exanodes cluster has delivered 2.3GB/s throughput.

Exanodes provides file systems with storage volumes (logical unit number or LUN) accessible in block mode.

Data is written to two different servers' disks so that if one fails the data is still available. This is called a RAIN or redundant array of independent nodes design.

However, because the storage servers are also application servers, they go down if the server is rebooted when, for example, its operating system is updated. A disk failure or server loss can trigger a data rebuild and Seanodes says a terabyte of data can be rebuilt in less than an hour. This minimises the risks of a second disk failure during the rebuild window. Such a repeated failure could cause data loss.

A similar rebuild with conventional disk arrays can take days.

Exanodes will work with any block storage devices, hard disk drives, SSD, RAID and external DAS and is the only any-to-any connect shared internal storage software on the market today.

There is a lot of additional storage management and data traffic on the server interconnect, particularly during a rebuild operation. Also, application servers will have processor and RAM resources used in storage processing, which could slow their application response.

Frank Gana, Seanodes' business development director, says: "When VMware aggregates, organises and consolidates CPUs in application servers, Exanodes aggregates, organises and consolidates storage devices in application servers."

Laura Dubois, IDC's storage software programme director, says: "The concept and benefits of an inside-out SAN are pretty obvious once you see them. All the aggregate formatted capacity is available to all the application computers. No stranded capacity exists and there is no single point of failure, since mirroring across computer systems would be employed."

The ECA (French Atomic Energy Commission) is a user of the product. A SIS product for a virtual machine environment is currently under development as is a port of the software to Windows.

Gana was unwilling to provide pricing information. He says "We do not want to commit exactly on the price". It depends upon the number and type of application and storage servers and the capacity of the storage involved. He says it is lower, very much lower, than an equivalent amount of traditional networked storage.

(For more on future storage trends, see "Web and grids set to shake storage scene", page 17)

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