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Poor quality controllers to blame, says Samsung

DailyTech reported several days ago that SSD manufacturers have been having problems with Samsung's latest generation of 32nm NAND flash. The new chips have slow write speeds, thus making them unsuitable for use in SSDs since that is one of the major advantages that the new drives have over conventional hard drives. 

We have received a reply from Samsung confirming the issue, stating that "for quality SSDs, every NAND process geometry upgrade requires a matching upgraded controller.  Should (Samsung's) 30nm-class NAND be used with a conventional controller of insufficient quality, performance slowdowns are indeed possible".

Flash memory stores information in arrays of memory cells made from floating-gate transistors. As these transistors scale to smaller process geometries, it becomes harder for electrons to flow. This sometimes causes errors in writing to memory cells which must be corrected through ECC (Error Correcting Code). ECC is typically handled on the flash controller, which may be overloaded by excessive write errors if it is not sufficiently powerful enough. This is the most likely scenario for what is happening.

Companies we spoke with confirmed similar problems with 32nm flash from Toshiba that had been overcome. Intel is using 34nm flash from IMFT that was delayed from mass production for six months, possibly due to a similar problem as well.

Most of the SSD manufacturers we spoke with had paired Samsung's flash with Indilinx's Barefoot flash controller. There are several iterations of the Barefoot controller out there for different SSDs, and no doubt Indilinx is working on the problem. However, it might take a while, and sharp price drops on SSDs are unlikely for several months.

Meanwhile, Samsung is currently in the process of completing a new flash controller revision for their own line of SSDs, and have not released any SSDs of their own using the new flash memory. Samsung states: "We spend many months developing and then fine-tuning the controller and firmware technology for our SSDs, working very closely with most of the major PC OEMs".



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RE: Errors?
By MatthiasF on 10/2/2009 5:11:06 PM , Rating: 4
One of two things could be happening.

First of all, the new NAND could require more than just EDAC for corrections, maybe also needing error scrubbing or perhaps even background scrubbing. If the memory controller itself isn't handling either, some of the tasks could be tossed up to the hard drive controller or even the CPU, slowing things down greatly.

Secondly, the new NAND being made by IM Flash Technologies (Intel/Micron) uses 3-bit per cell and not MLC, which needs a slightly different controller design.

Here's a helpful video explaining some of it.

http://www.micron.com/media/2009mediakit/3bitmlc_m...


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