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