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Spoke to Micron about NAND and SSD

Discussion in 'Hardware' started by ryanjleng, 11 Feb 2008.

  1. ryanjleng

    ryanjleng ...

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    The following is a transcript of my conversation with Kevin Kilbuck, Senior Marketing Manager, NAND Market Development at Micron Technology.

    The interview took place over the phone on 2008-01-09. 7:45AM US PT.

    Here's part of the material to share with you, all of whom i learn so much from over the years. Here's something to give back to you all. THANKS! :)

    --------------------------------
    Introduction Material
    --------------------------------
    NAND Flash memory is ubiquitous. It is currently being used in solid state storage devices ranging from USB Flash Drive, Memory Stick, Secure Digital (SD) and Compact Flash (CF) cards, Solid State Disks (SSD) and more.

    These flash devices can be found in computers, GPS units, cameras, automotive navigation systems, mobile phones, televisions, entertainment systems, networking and telecommunication equipments, industrial machineries and even the humble phone and fax machines.

    NAND memory can be separated into 2 fundamental types. Single-Level Cell (SLC) and Multi-Level Cell (MLC). Each has its’ own advantages as stated below.

    --------------------------------
    NAND SLC
    --------------------------------
    Read/Write Speed: Fast
    Read: 25 micro-second
    Write: 200 micro-second
    Memory Capacity: Lower
    Memory Block size: 64 pages
    Writing/Erase cycles: High (100,000)

    --------------------------------
    NAND MLC
    --------------------------------
    Read/Write Speed: Slow
    Read: 60 micro-second
    Write: 800 micro-second
    Memory Capacity: Higher
    Memory Block size: 128 pages
    Writing/Erase cycles: Low (5,000 to 10,000)

    * These numbers are based on 50nm Generation of NAND.
    ** Source: Flash Memory Device, TDK Corp.


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    The Q&A
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    1. How important is NAND technology in Micron’s future?
    Kevin Kilbuck: It is very important for a lot of the reasons. Fundamentally, we are now using NAND as our process driver for our memory. So, we will bring up a new process with NAND flash device, first in our R&D fab then our production fab.


    2. Is Micron focusing on SLC or very much into MLC? What’s the distribution like between these NAND technologies?
    Kevin Kilbuck: Well, when we started in NAND flash, we were 100% SLC. We first introduced our NAND MLC products in 70nm process and now we are on the 50nm process. We caught up the market leaders in terms of density.

    We plan to have a two prong strategy. One is to be up there with the leaders in highest density and lowest cost MLC products, and also to have a somewhat differentiated portfolio with broad SLC products.

    The way we think the market is shaping up, is applications that can use MLC NAND will use it because they want the lower cost and are willing to tolerate lower number of write cycles, and lower performance as well. Then, there are applications that have to have SLC either for reliability or performance reason, or both.


    3. Will the Solid State Disks be based on SLC NAND?
    Kevin Kilbuck: Yes. Today the limited market out there is 100% based on SLC. We do currently offer a portfolio of SSD products.

    There are discussions in the industry about whether MLC NAND in SSD would be good enough for certain applications. The big one out there with a big question mark is whether MLC is good enough to go into a notebook PC. In a notebook PC, there is significant writing involved, but the question is whether the MLC write signaling capabilities combined with a good controller design that has proper amount of wear leveling, will that be good enough. The notebook PC manufacturers dictate that SSD’s lifespan has to be on par with the standard hard drive, which has a guaranteed operation life of at least 5 years. If we can provide the same guarantee based on a MLC based drive than I think we will see wide spread SSD usage in the notebook PC market. For this to happen, we are really going to be relying on the controller and there may be a need for changes in the operating system as well.

    A lot of the prevalent operating systems out there tend to do a lot disk trashing. They are writing very small block sizes whenever they need to. Writing very frequently but in small amount of data to the drive is not conducive to NAND. NAND wants to do lots of large write and then stop for a while.


    4. Will there be a hybrid of SLC and MLC NAND in a Solid State Disks?
    Kevin Kilbuck: That is a possibility. If you could partition it so that the data you’re writing a lot like the partition tables and LBA are located in SLC NAND. But, that would also require some changes to the firmware and controller to be able to partition that. I will say that is still in the air whether MLC or a hybrid version would be used in SSD.

    Clearly in enterprise based applications, it is much more write-intensive environment and there are reliability concerns. So, we are pretty convinced SLC is going to be around in the enterprise market. SLC is also performance proven.


    5. There was one strange concerned that was brought up when we talked about SSD was the ease of data recovery on an aging or dead SSD. Is it a situation once the data is gone, it is irrecoverable?
    Kevin Kilbuck: No, typically the way NAND flash works when writing is that it will send a program command to the NAND. It will keep trying to write until it exceeds some maximum specification. When that happens, the byte, block or sector of the drive will be marked as failed and no longer be writable. So then that data will be written to another portion of the flash. There is no data issue. What happen in a NAND based SSD is that over time, you will loose capacity.


    6. So there is some kind of dynamic scaling down of capacity?
    Kevin Kilbuck: Yes. Again, this would probably require some firmware changes. It is kind of like a battery meter on your laptop. You can have a SSD ‘capacity’ meter. I mean, you probably can ignore it for several years but you can get some kind of warning saying you have lost a gigabyte of capacity and you might want to replace the drive next year or something.

    So I guess the simple way to say it is that NAND wears our gracefully instead of crashing.
     

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