Enterprise Flash Cache-ing Up To HDDs

Although the well-documented shortageof hard disk drives led many industry watchers to believe there would be a significant move to solid-state drives (SSDs) at the end of last year, that actually hasn’t been the case because many OEMs ordered excess inventory of SSDs. SSDs' higher cost compared with HDDs also makes lumping the two in the same category unfair.

"I don't see any significant replacement of HDDs with SSDs ... [it is] no such elastic purchase,"’ says Mark Peters, a senior analyst at Enterprise Strategy Group. "If you want a minivan or sedan, you're unlikely to replace it with a sports car. I'm sure there are examples of it happening, but it's neither significant nor a trend."

Flash and SSDs have been largely deployed to help with specific workloads (such as databases, OLTP and generic server virtualizations), but Peters says ESG is seeing a pretty rapid shift toward flash/SSD being used in a cache manner--meaning that the workloads become that much broader. He adds that this appears to be the main approach enterprises will use them for going forward. But solid state uptakein the enterprise has been far higher than what Storage Strategies NOW predicted last year.

Price comparisons depend, says Peters, because there is not just one type of HDD or flash. He says there is near parity in terms of cost per gigabyte, allowing for compression and dedupe on an all-flash appliance when compared with high-performance disk, or a factor of 10 to 50 times for cheap, fat SATA compared with high-performance, server-based solid state. But businesses need to determine which metric to use to compare price--cost per gigabyte, per IOPS or power consumption, Peters says. If an enterprise is using high-performance disks, SSDs tend to be more cost-effectiveto implement than 15,000-rpm hard drives because it takes fewer SSDs to provide a given number of transactions per second.

However, SSDs are starting to have a major impact--more consumer and business products will make a switch from using HDDs to only using SSDs or flash memory, some industry watchers predict, even if the cost is higher. They maintain that flash holds great appeal for mobile devices and automobile applications because it can be put into smaller volumes than HDDs.

To drive further enterprise SSD adoption, there has to be greater understanding of its capabilities, combined with growing choice, market acceptance and experience, Peters says. The growth areas for SSDs will be mainly in client computing applications and in enterprise applications where SSDs can provide fast transaction processing, partly to support cloud services and storage in the cloud.

Almost all major enterprise storage vendors now offer SSDs as part of their storage tiers, and several companies offer pure flash-based appliances. But HDDs will continue to have a significant role, supplying inexpensive mass storage. A blending of the two to combine their strengths, observers say, makes sense. The addition of a flash storage hierarchy results in greater application performance: Applications can access the most-used data more than 100 times as fast as when it is stored on a combination of enterprise SSDs and HDDs.

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