DRAM – The SSD Guy Blog

Flash vs. DRAM in PCs – Flash Wins

Some time ago Objective Analysis ran nearly 300 standard benchmarks on a PC with varying amounts of flash and DRAM and found that a dollar’s worth of flash provided a greater performance boost than a dollar’s worth of DRAM once the DRAM size grew above a certain minimum (1-2GB) depending on the benchmark.

You might wonder how this could possibly be true. Everyone knows that best way to improve any computing system’s performance is to add DRAM main memory. How could flash, which is orders of magnitude slower than DRAM, provide a bigger performance boost than DRAM?

It all makes sense if you think of the DRAM of something that is there only to make the HDD look faster. More is better, but if you can use a little less DRAM and add a large flash memory layer then disk accesses appear to speed up even more.

The benchmark data and the price/performance findings that are Continue reading “Flash vs. DRAM in PCs – Flash Wins”

Kaminario’s Performance and 7-Year Flash Life Warranties

Today Kaminario added a performance guarantee and a 7-year warranty to its arsenal. The company introduced its “Consistency Under Failure Guarantee” which ensures customers will see no more than a 25% drop in performance during a system failure. This means that critical operations and applications can continue to run at near-standard performance despite the failure of an SSD or even an entire node. Kaminario president Dani Golan told The SSD Guy last week that this is a conservative guarantee, and that few customers see more than a 10% degradation during failure tests in their own production systems.

As for the 7-year flash endurance warranty, no matter which SSD Continue reading “Kaminario’s Performance and 7-Year Flash Life Warranties”

IBM Completes Texas Memory Systems Acquisition

IBM announced on Monday October 1 that it had finalized its acquisition of Texas Memory Systems (TMS.) This transaction was first announced in mid-August and was analyzed at that time in an Alert sent to Objective Analysis clients.

Here are a few salient points from the Alert:

TMS is the world’s oldest SSD maker, and has recently made an aggressive move from DRAM to NAND flash, providing very high performance PCIe SSDs and arrays.
TMS and IBM play into the same market: storage for large-scale computing. Their technologies complement each other, since IBM’s current solid state storage offerings were lightweight compared to those of TMS.
The acquisition meshes with IBM’s mantra of “Smarter Planet, Smarter Storage, and Smarter Computing.” SSDs improve storage speed while reducing power and space requirements.

Objective Analysis sees this as a good fit that will harness the synergies of two very similarly managed companies to produce very positive results.

How Controllers Maximize SSD Life – External Data Buffering

Since NAND flash is weakened by erase/write cycles then it would make sense to try to reduce those cycles to prolong the life of an SSD right? That’s what external data buffers are designed to do.

There are many ways to use RAM (either a RAM internal to the SSD controller chip or a discrete DRAM chip on the SSD’s printed circuit card) to stage data in a way that will reduce erase/write cycles.

One is to perform a function called “Write Coalescing.” This involves Continue reading “How Controllers Maximize SSD Life – External Data Buffering”

An ReRAM SSD Design

A colleague pointed The SSD Guy to an ExtremeTech article about researchers at Japan’s Chuo University who have designed an SSD that uses a resistive RAM (ReRAM) as a buffer and is built using TSV technology. The design was presented at the IEEE’s 2012 Symposium on VLSI Circuits this month in Hawaii. A Nikkei article gives additional information.

The basic architecture reminds me of an FRAM + NAND SSD design that a Korean university presented at the Flash Memory Summit a few years ago. Either approach gets past the problem of using a failure-prone battery, a temperature-sensitive supercap, or a big bulky bank of Continue reading “An ReRAM SSD Design”

DRAM vs. SLC SSD – Which Makes More Sense?

The SSD guy usually argues that NAND flash (as an SSD) fits into the memory/storage hierarchy for two reasons:

SSDs are cheaper than DRAM but more expensive than an HDD
SSDs are slower than DRAM but faster than an HDD

An SSD is usually a very good alternative to adding more DRAM to a system, but this is not always the case. Users need to look carefully at the SSD they plan to use to make sure they are getting the most for their system spend. Continue reading “DRAM vs. SLC SSD – Which Makes More Sense?”