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Will There Be Tiers Of SSD?

I heard at Storage Networking World (SNW) that once storage finally moved to Solid State Disk (SSD) and there were no longer mechanical drives, there would be no more need for tiered storage. Everything will be on SSD, it will all be fast and no one will care. Will SSD end the need for proper data management or will there be tiers of SSD?

First, while SSD prices continue to plummet and capacities continue to rise, it will be years if not decades before mechanical drives are replaced in total. While PCI-E based SSDs from companies like Texas Memory or Fusion-io have taken significant steps to lowering SSD costs, the technology is still proportionately more expensive than their mechanical drive counter parts. Automated tiering technologies from companies like Storspeed, Avere and Dataram also promise to be a stepping stone for the broader market to adopt SSD by maximizing the use of a smaller amount of non-mechanical storage.

Even before mechanical drives are replaced we will see tiers of SSDs; we have it now. There is a clear performance difference in write speed of DRAM based SSDs and Flash based SSDs, although that gap is closing. There is also the price and reliability difference in single level cell (SLC) based SSDs and multi-level cell (MLC) based SSDs. SLC is considered the enterprise class SSD; it typically has faster write speeds, lower power consumption and better write endurance.

MLC on the other hand has a significant cost advantage by being able to squeeze more capacity in the same space. Several vendors are now trying to make MLC more practical for the enterprise by batch selecting MLC chips for better write endurance. To some extent I expect they will succeed. MLC may become the SATA drive of SSD drives.

With these examples you can make a case for three tiers of SSD: DRAM, SLC Flash and MLC Flash. This does not factor in all the new memory technologies that are on the horizon. The point is that even when SSDs become the predominant storage platform, and before that, certainly as that evolution takes place, there will be tiers of SSD. Storage Managers are going to need to leverage techniques like those we discussed in our article "Integrating SSD and Maintaining Disaster Recovery" to manage those or implement an automated tiering technology like those we discuss in "Fixing Application Storage Performance".

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