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Tandberg promises safer storage with fewer discs

Tandberg ASA's InoStor subsidiary has invented a new RAID system, which it claims uses fewer discs than RAID 5+1 but is just as effective at protecting data.

The RAIDn system is actually a library of software algorithms that provide protection against multiple drive failure by using a parity system (a data check on each chunk of information).

InoStor has embedded the technology into a line of Linux-based network-attached storage (NAS) appliances, and is now looking for licensees to use the RAIDn technology.

"By configuring an extra drive RAIDn provides greater protection than RAID 5," said David Licosati, InoStor's vice-president of business development. "Without mirroring, administrators can add three inexpensive disc drives using RAIDn and obtain the same reliability as RAID 5+1, today's best high-availability - and most expensive - storage scheme."

How is this claim justified? In RAID 4, data discs have parity data about their contents stored on an additional disc so that if a data disc fails its contents can be reconstructed from the parity data. The parity disc is a bottleneck. In RAID 5, the parity data is spread across all the data discs to get rid of the bottleneck.

If we have four data discs originally then in RAID 4 we would have five discs in total. With RAID 5, we would also have five discs in total for the same amount of data.

In RAID 1, the data discs are mirrored but this requires twice the number of discs. Mirroring is more effective and provides faster read access than RAID 4 or 5. Plus, if two or more drives crash RAID reconstruction can fail.

Mirroring solves that. You can add mirroring to RAID 5 - called RAID 5+1. With four discs' worth of data and one disc's worth of parity, that means five discs for mirroring and so 10 discs in total.

RAIDn technology can supply that same protection by with only seven discs, InoStor claims. So it is more cost-effective than RAID 5+1 but more expensive than cheaper RAID systems offering less protection, such as RAID 4 or RAID 5.

This is in theory of course because you can't actually buy RAIDn technology from anybody but InoStor and you can't buy it on its own. InoStor sells it embedded in its own NAS boxes.

The 720Gbyte ValuNAS 9100 is priced at about $5,700 (£3,200) and InoStor claims it outperforms Dell's 725N NAS box which is priced at $3,000 for 480Gbytes. Clearly Tandberg isn't selling RAIDn cheaply.

RAIDn has the added property that it can be configured at multiple RAID levels - you don't have to set it at the RAID 5+1 equivalent.

Licosati envisages RAIDn "becoming an industry standard". This may be optimistic as the technology has been known about for more than a year.

Chris Mellor writes for Techworld


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