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How SSDs Work

SSD 102: The Ins And Outs Of Solid State Storage
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With the internal SSDs we're discussing today, flash memory and a controller are installed onto a printed circuit board (PCB) and packaged into a small enclosure. This housing is typically in one of the 1.8”, 2.5”, or 3.5” form factors that we all know and love from conventional hard drives. These can be mounted into PCs, laptops, or certain rackmount server environments. Indeed, flash SSDs look and largely behave like hard drives, with the exceptions that there are no moving parts and they weigh less. In addition, modern SSDs require very little cooling. Most SSDs employ a 2.5” housing and utilize 3 or 6Gb/s interface speeds.

MLC and SLC NAND Flash

Internally, all flash SSD products store data onto either single-layer cell (SLC) or multi-layer cell (MLC) NAND memory, able to store a single bit or multiple bits per cell, respectively. SLC cells offer less capacity per transistor than MLC, but higher write performance and data durability.

Modern Controller Architectures

All SSD designs are based on flash controllers that drive the storage circuits and connect to the host system via Serial ATA. Modern designs utilize the controller "brain" to tackle various needs. For example, data durability is addressed through wear leveling algorithms, ensuring that flash memory cell usage distribution is as even as possible to maximize the device’s life span. Performance is optimized through multiple flash memory channels, load balancing, and different methods of caching. Some controllers have an integrated cache, others work with a separate DRAM memory chip, and other designs utilize a part of the flash memory across multiple channels for data reorganization. Please read the article Tom’s Hardware’s Summer Guide: 17 SSDs Rounded Up for more details on architectures and specific products.

Trend: Toggle DDR NAND Flash

Samsung introduced Toggle DDR NAND flash memory a few months ago. This is a flash memory design that transfers data during the rising and falling edge of a memory signal, much like DDR DRAM. This approach debuted in the enterprise segment but will soon also be available in consumer SSDs. The main benefit of Toggle DDR is its increased bandwidth of 66 to 133 Mb/s per channel as opposed to 40 Mb/s. Drives using the new approach will probably not employ the faster peak bandwidth, but will instead try to maximize SATA II performance on 3 Gb/s interfaces while further lowering power consumption. We’ll explain in a bit why this is important.

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  • 0 Hide
    another alex , 12 September 2010 19:54
    "Solutions with 8+ GB of RAM and RAM drives to hold the swap file are the more elegant and higher-performing approaches."

    Really? Putting the swap file on a RAM drive is a good idea? I'd like to see more in-depth investigation into this, as my understanding is that the swap file is there to keep memory pages that have been swapped out of physical RAM to free up more space. If that is changed to effectively mean moving them from one bit of RAM to another bit, then it nullifies the whole point and you'd be better off setting a 0 size swap file and leaving that RAM available for normal use.
  • 0 Hide
    david__t , 13 September 2010 19:56
    ^^ I totally agree with that , however some programs and games simply do not work without a swap file. Theoretically if you did have 8GB+ then you shouldn't use the swap file at all, however everything I read always recommends leaving this turned on regardless of system specs. Still, moving data around from one memory area to another is vastly superior to that of memory to hard disc and back again - if nothing else, it frees up SATA bus bandwidth.
  • 0 Hide
    sirkillalot , 14 September 2010 00:06
    im still not convinced to get a ssd imm i guess a wd vraptor will do 4 now
  • 0 Hide
    proletarian , 14 September 2010 13:52
    i've been considering an ssd for a while, no point jumping just yet, gonna look at the market a bit longer, looking at a few drives, all 120gb models, gonna grab em when they're being replaced.
  • 0 Hide
    jamie_macdonald , 14 September 2010 16:45
    I jumped to a Vertex 120gb (v2) about a month back ... apart from paying £270 for such a small drive i don't regret it ...the time saved has payed for itself allready and the responsiveness of the OS is like awesome..

    ..only holdback if you cannot afford it ...cause the more that can and do .. the better for all of us.

    if me "biting the bullet" means the cost will come down in the end then it'll all have been worth it ...and if not worth it for that fact, least i have enjoyed some PC advancment ..something i had waited a long long time to do watching the prices fall and the drives get faster..

    if you can ... get one ... all i can say :) 
  • 0 Hide
    jamie_macdonald , 14 September 2010 22:52
    >.>

    Loving the spam ..lol
  • 0 Hide
    Ko0lHaNDLuKe , 15 September 2010 07:59
    They are still way too expensive for me to even consider getting one!
  • 0 Hide
    Rab1d-BDGR , 15 September 2010 18:18
    Quote:
    Given that modern controllers take care of write distribution, and file deletion won't always trigger physical deletion of blocks, it's advisable to plan a secure erase strategy for drives that are to be decommissioned in the future. Tools such as Secure Erase 4.0 are helpful.


    I find tools such as a lump-hammer quite effective too... ;-)
  • 1 Hide
    gdilord , 15 September 2010 18:43
    david__thowever some programs and games simply do not work without a swap file.
    Setting the swap file to 2MB is an effective work around in many cases.
  • 0 Hide
    ignoramus , 17 September 2010 00:12
    @gdilord
    Unless you can break the silicon (not just the packaging) into quite small pieces it is usually possible to recover data from a flash memory. On the other hand, a sufficient sequence of repeated (erase + random over-write) is hack-proof