Networked storage a thing of the past?

by Chris Mellor

November 23, 2007 —

French startup Seanodes has a product to combine 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 IDC's
term, 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 1TB
of data can be rebuilt in less than an hour. This minimizes 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, said: "When VMware
aggregates, organizes and consolidates CPUs in application servers, Exanodes
aggregates, organizes and consolidates storage devices in application servers."

Laura Dubois, IDC's storage software program director, said: "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, and said: "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 said it was lower, very much lower, than an equivalent amount of traditional
networked storage.

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