How-To Match Flash Memory Solutions to Application Needs

By Narayan Venkat, Violin Memory, for, CRN May 04, 2012

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1. PCIe Cards
This option packages as much flash as possible onto a PCIe card that plugs into a high speed slot on a server. Instead of a slow disk, it’s a large capacity memory resource to feed hungry CPU cycles. Because of their much higher interface speeds, PCIe cards have much better performance than a typical commodity SSD. Through smart design, it can build in certain flash-optimized hardware and software features.

This solution is most commonly viewed as a memory extension that’s cheaper and denser than DRAM, while making a single host server run faster. Because PCIe cards are tied to a host server, there are reliability concerns in its inability to be deployed as shared network storage. Cost is a factor as well. A single PCIe card is typically two to three times the cost of the server and can double your overhead if mirroring is needed for reliability.

2. Solid State Disk (SSD) Solutions
Commodity SSDs are a natural evolution from consumer flash devices. The concept is straightforward: a device with the same form factor of an HDD that uses the same connectors and interfaces and can be plugged into a server or disk array. Multiple SSDs can be combined into a disk array to boost performance with little change needed to the surrounding hardware and software. Applications think they are seeing a faster disk drive.

While SSD solutions are convenient in that the ability to ‘look like a fast disk’ simplifies things, it overlooks the key issue that flash is a very different media than rotating magnetic disk. The commodity SSD is not meant for a use case that is focused solely on performance. Rather, it's designed to take advantage of the commodity cost and associated commodity reliability. That tradeoff means the surrounding hardware and software is not optimized for the unique characteristics of flash.

HDD arrays don’t need to account for flash specific issues, such as garbage collection and wear management and hence treat the devices as a black box. A controller designed for an HDD array can easily become the bottleneck, reducing the performance benefit.

3. Flash Memory Arrays
Flash packaging has a significant impact on the strength and weaknesses of a given solution. Flash Memory Arrays take the approach of designing a system from the flash chip up to better manage the balance of performance, reliability, and cost to optimize for enterprise storage. By starting at the flash chip level, vendors can optimize hardware, firmware, and software for the unique characteristics of flash. A purpose-built system such as that can very efficiently pool flash resources within the system for superior performance density and aggregate multiple systems for scalable shared network storage. Given the emphasis on efficient flash aggregation, a memory array is likely to be suited to a use case where a faster disk drive will do the trick.

Solution providers who are armed with the information to help their clients sort through the myriad of technology options on the market become valuable business partners. The best ones consistently get the round peg in the round hole. Flash storage is similar to all strategic technology decisions in that there are pros and cons to the various approaches.