This is quite the time for Flash-based solid-state drives (SSDs)! Seagate just dropped into the market and whenever a heavyweight like Seagate drops in, there’s a big splash. We’ll cover Seagate in a later blog (you can already read all about it all over the Web) but the announcement helps lead into a discussion of the live (!) SSD seminar that distributor Bell Micro has just taken across North America. The road show landed in Milpitas earlier this month and the keynote speaker, storage analyst extraordinaire Jim Handy, did such a great job of covering the topics of interest to server designers and enterprise system architects that it will take several blog entries to cover all of the information.

For this blog entry, we’re returning to the Flash Zone, a concept described by Denali Software’s CTO Mark Gogolewski in his keynote speech—The World is Flash: A Disruption of the Memory & Storage Hierarchy—at Memcon 2009. The Flash Zone is the name put to the performance gap between DRAM and disk storage. There’s not only a gap in performance within the Flash Zone, there’s a transition from volatile memory (DRAM) to non-volatile storage (hard disk). With steep cost/bit price declines and per-device capacity growth, NAND Flash devices now easily fit into this gap and produce a new and viable layer in the overall computer memory hierarchy.

What’s new is that Jim Handy’s keynote at the Bell Micro SSD seminar put some welcome numbers on the Flash Zone that further clarify Flash’s place in the hierarchy. Here’s an image of that particular slide.

This image plots the performance and cost of the different memory hierarchy layers from first-, second-, and third-level processor cache through DRAM, disk, and tape. Because Handy’s used a log-log scale to plot everything, the graph looks nice and linear even though the reality is quite a bit messier. For a conceptual graph however, this’ll do nicely.

Note that there’s a gap in the hierarchy. That’s the Flash Zone. Here’s the same plot augmented a bit. The big red circle identifies the Flash Zone.

Also note that Handy has labeled the gap and says it’s “growing.” The gap’s growing because DRAM is getting faster, bigger, and cheaper, moving its ellipse up and to the left while HDDs are getting bigger, although not much faster, moving the HDD ellipse horizontally to the left. The result is a growing performance and bandwidth gap between DRAM and HDDs.

Flash fits into this gap very, very nicely said Handy (and as discussed in this blog previously). Later in his keynote, he displayed this image to underscore the point.

There are currently at least three ways to fill the Flash Zone in a memory hierarchy using NAND Flash memory. The first way, the way that gets the most attention these days, is with solid-state drives (SSDs). Because they employ the same interfaces and share the same form factor with HDDs, SSDs are an easy, drop-in Flash Zone filler. They boost performance just by dropping them into place as HDD replacements, although that may not be the best way to introduce SSDs into the hierarchy. (More about that in a later blog.)

The second way to drop NAND Flash memory into the Flash Zone is through direct- or I/O-attached drives. This is the approach advocated by Fusion-io, as discussed in that earlier AgigA Tech blog entry on the Flash Zone. Direct-attached SSDs eliminate the HDD interface and protocols, which were designed with built-in assumptions about the performance characteristics and limitations of HDDs (“rotating rust” quipped Scott Stetzer, VP of Marketing at SSD vendor STEC). Free of those limiting assumptions and limits, direct-attached SSDs deliver more performance than do SSDs employing HDD interfaces.

Handy showed the ways to introduce these two types of SSDs with the following slide:

In enterprise-class server systems, SSDs with HDD interfaces typically plug into SAN racks and tie to servers over a network while direct-attached SSDs plug directly into the server over a high-speed interface (typically PCIe). Note that smaller servers with HDD interfaces often talk to SSDs directly.

Because he was speaking at an SSD seminar, Handy did not discuss the third way of introducing NAND Flash into the Flash Zone—the approach employed by AgigA Tech’s AGIGARAM. That approach mates the NAND Flash directly to the server’s DRAM, creating a high-bandwidth connection between the two memory hierarchies. In this application, however, the NAND Flash is used for DRAM backup and power-failure bulletproofing—not necessarily for storage (although there are other possibilities to be discussed in this respect).

So far, we’ve only been able to discuss two of Handy’s 47 keynote slides. The talk contained a ton of good information for server designers and enterprise system architects. More later.

Note: Handy’s keynote was based on his company’s new report: Solid State Drives in the Enterprise – 2010.