Controllers become the focal point for solid-state disk

As the use of flash memory for solid-state disk progresses, vendors who make SSD controllers are also worth watching. Fusion-io is one who just announced a major advance.

John Webster Special to CNET News
John, a senior partner at Evaluator Group, has 30 years of experience in enterprise IT storage, spanning mainframe and open systems environments. He has served as principal IT adviser at Illuminata and has held analyst positions at IDC and Yankee Group Research. He also co-authored the book "Inescapable Data Harnessing the Power of Convergence."
John Webster
3 min read

Warning: This post is larded with acronyms. Sorry, it can't be helped.

Fusion-io recently announced SMLC flash memory. What is SMLC? To understand how Fusion-io coined this acronym (and it is all theirs), you need to first become familiar with two more--SLC for Single Level Cell and MLC for Multi Level Cell. Both refer to types of NAND flash memory, and both are hot items right now, but for different reasons. MLC NAND flash memory is relatively cheap, abundant, and commonly used in PCs, laptops, and mobile messaging devices. SLC is in comparison much more expensive, not as abundant, but is also hot because it is now being used to replace spinning disk in high-performance storage arrays by a growing list of vendors that now includes EMC, HP, and NetApp to name just three.

Fusion-io's SMLC is not actually a new addition to the flash memory family. (Fusion-io doesn't make flash.) SMLC is more like an attribute or feature, if you will, of a new solid-state disk controller that Fusion-io has introduced. What this new controller does is in essence give MLC flash the characteristics of SLC. Hence SMLC stands for Single-mode Multi-Level Cell.

Fusion-io Logo Fusion-io

Here's why that's significant. NAND flash has a shortcoming vs. disk as a storage medium in that you can't use it to store new bits of information over the same time period as disk. NAND flash begins to "wear out" faster than disk the more you write new data. This problem is more severe with MLC than SLC. At least one disk drive manufacturer says that this shortcoming plus some others makes NAND flash unsuitable for enterprise data center applications.

Undaunted, enterprise datacenter storage array vendors have gone ahead and implemented NAND flash-based SSDs and data center customers are buying them. These implementations use SLC because its longevity and reliability characteristics are better than those of MLC. However, as mentioned, SLC is more expensive, so the high-end array vendors are trading-off lower-priced SSD components for better performance, reliability, and longevity--a reasonable trade to make given the intended application. That makes SLC-based SSD less attractive. (Sorry, see death-by-acronym disclaimer above.)

Suppose however, that MLC could be given the more data center quality characteristics of SLC. The trade-off then goes away. That's the value proposition supporting Fusion-io's SMLC. The secret sauce here gets poured into Fusion-io's SSD controller. New controller-resident processes add the needed performance, reliability, and longevity to MLC, making it roughly equivalent to SLC in function, but at a far lower price point.

How significant could this introduction be? SSD for the corporate data center has always been hampered by price. In fact, even though data center SSD arrays are blazing fast, they have struggled to compete with disk arrays for decades. Even recently as customers are now looking seriously at the new flash-based SSD implementations from Intel, Texas Memory Systems, and others, price remains a stumbling block limiting SSD to address only the applications needing the best I/O performance. Lowering the price-point significantly, as Fusion-io does with this announcement, allows flash-based SSD to address a broader range of applications and replace disk in greater volume.

Beyond the threat this announcement poses to rotating disk, RAID (redundant array of inexpensive disks) as we know it is also threatened. Fusion-io's controllers can be clustered across physical boundaries to form server-internal storage networks. Data can be quickly mirrored across these boundaries yielding a solid-state storage subsystem with data protection that could compete on price with a RAID array.

To date, Fusion-io has OEM (original equipment manufacturer) relationships with Dell and HP. IBM has announced its Quicksilver project based on Fusion-io technology, but has not as yet delivered product bearing Quicksilver technology. SMLC will be available this quarter for Fusion-io's ioDrive and ioDrive Duo controllers. While these OEMs have yet to announce SMLC support, I expect the announcements to be forthcoming.