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SSD could ultimately replace hard disk drives, Hitachi CTO says

Faster servers threaten to drown today's storage systems

By , Network World
January 22, 2010 04:58 PM ET

Network World - Flash-based memory is still too expensive to be a data center's primary storage technology, but solid-state disks may ultimately replace mechanical hard disk drives, says Hitachi Data Systems' CTO Hu Yoshida.

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Thanks to Moore's Law, the speed of server processors is advancing so fast that they threaten to "“drown" storage systems, which have a slower improvement rate. While disks are doubling in capacity every 18 months, in accordance with Moore's Law, the cost per capacity is only dropping 30% a year, and speed improvements are not keeping pace with servers, Yoshida said in an interview about storage trends with Network World.

There's still a 10- to 12-year development road map ahead for spinning disk drives, but the technology's inherent limitations will eventually force a shift to something new, Yoshida says.

The spinning disk is "probably the only high technology that's still very mechanical," Yoshida says when asked why cost per capacity is improving slowly. "It has a motor that spins and it has an arm that has to be moved to the right track. There is a limit to how fast we can spin that disk."

Enterprises have begun using small amounts of flash-based solid state disks to serve applications whose performance needs aren't met by mechanical hard drives. SSD can be anywhere from 10 to 17 times faster than hard drives, while also costing 10 to 20 times more, Yoshida says.

While the price can be expected to drop, Yoshida says it may not happen as fast as some people expect. Flash is not produced in the same types of quantities as spinning disks and it will therefore be hard to eliminate the price gap between SSD and hard drives, he says.

However, it is possible that flash will someday overtake hard disk drives as the primary data storage technology. "Eventually, the thought is that some sort of solid state disk will replace [spinning disk drives]," Yoshida says.

But the flash technology used in enterprise storage products today can wear down after about 100,000 writes, Yoshida notes. Vendors are trying to make flash more durable, but ultimately it may not be enough to make flash a suitable replacement for hard disks, Yoshida suggests. Other non-volatile storage technologies, such as PcRAM, are in development and might ultimately prove to be more durable, he says.

Because hard disk drives are in such wide use and will be for the foreseeable future, vendors are pursuing several strategies to make them more efficient. One such strategy is striping, which spreads data across a wider pool of storage devices. Thin provisioning, meanwhile, over-allocates storage to servers, which allows faster provisioning of space to servers without actually adding more capacity.

Another important technology is a global cache, which allows multiple storage processors access to the same cache, Yoshida says. Such technology is available in Hitachi's USP V, the EMC DMX and IBM DS8000, he says.

More advances will be needed, because various trends are placing more stress on storage systems. While the demand for physical storage space rises constantly, increasingly powerful servers are also demanding more data serving capability.

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