Hey, There’s an Elephant in the Room

When the first X25-M reviews went live a few people discovered something very important, something many of us (myself included) missed and should’ve addressed: the drive got slower the more you filled it up. It’s no great mystery why this happened, but it seemed odd at the time because it went against conventional thinking.


LegitReviews was one of the first to spot the SSD slowdown phenomenon, good work Nate.

It’s worth mentioning that hard drives suffer from the same problem; just for a different reason.

Hard drives store data on platters; the platters rotate while an arm with read/write heads on it hovers over the surface of the platter and reads data while the platter spins. The diameter of the platter is greater the further out on the platter you go, that’s just how circles work. The side effect is that for the same amount of rotation, the heads can cover more area on the outside of the platter than on the inside.

The result is that transfer speeds are greater on the outer sectors of the platter than on the inner ones. OSes thus try to write as much data to the outer sectors as possible, but like beachfront property - there’s only a limited amount of space. Eventually you have to write to the slower parts of the drive and thus the more full your drive is, the slower your transfer rates will be for data stored in the innermost sectors.

Fragmentation also hurts hard drive performance. While modern day hard drives have gotten pretty quick at transferring large amounts of data stored sequentially, spread the data out all around the platter and things get real slow, real fast.

Randomness is the enemy of rotational storage.

Solid state drives aren’t supposed to have these issues. Data is stored in flash, so it doesn’t matter where it’s located, you get to it at the same speed. SSDs have +5 armor immunity to random access latency (that’s got to be the single most geeky-sounding thing I’ve ever written, and I use words like latency a lot).

So why is it that when you fill up a SSD like Intel’s X25-M that its performance goes down? Even more worrisome, why is it that when you delete data from the drive that its performance doesn’t go back up?

While SSDs are truly immune to the same problems that plague HDDs, they do also get slower over time. How can both be true? It’s time for another lesson in flash.

Why You Should Want an SSD The Anatomy of an SSD
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  • Slash3 - Wednesday, March 18, 2009 - link

    Page 29: "Not all applications will launch faster than a VelociRaptor on a SSD, but let's not forget that the VelociRaptor is the world's fastest hard drive."

    Really? What about the nice and speedy enterprise-level 15k SAS/SCSI drives everyone neglects to acknowledge? :)
    Reply
  • George Powell - Wednesday, March 18, 2009 - link

    I believe it refers to consumer drives. While SAS drives are beginning to be a possibility on the desktop with newer motherboards supporting them natively, the drives themselves are too expensive and too noisy for most consumers to actually want them.


    Reply
  • FishTankX - Wednesday, March 18, 2009 - link

    Good info. However, I noticed one mistake.

    Second page
    Samsung had a MLC controller at the time but it was too expensive than what SuperTalent was shooting for.
    Reply
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  • matrixireland - Thursday, December 24, 2009 - link

    hi would like to know what you pros think of the;
    Golden Leopard ASAX-ZIF1.8-SSD? what would you add to it?
    And how would you rate it against other ssd?

    Specifications:

    product description

    ASAX-ZIF1.8-SSD is a high-performance design solid state drive based on the high-end micro-control IC with flash memory storage medium integrated advantaged of high speed,convenient ,aseismatic,energy-saving etc.


    specification

    Model

    Size

    Interface

    Material
    ASAX-ZIF1.8-SSD

    1.8inch 70×54×6mm

    ZIF
    Aluminum-magnesium alloy appearance ,drawbench and colorful oxidation surface,elegant temperament


    performance
    read speed:80- 96Mbytes/second write speed:50- 60Mbytes/second
    support ATA-7 V3 PIO/multi word/ultra DMA MODES
    Low power TFBGA,4 channel of flash controller,masked ROM and data SRAM
    SAMSUNG flash keeps the data faster on reliability and endurance
    Dynamic and static wear-leveling prolong NAND FLASH and SSD for longer life
    8/16 bit BCH ECC data error correction ability effectively guarantee the data read security.

    Design consideration

    Capacity

    16G/32G/64G/128G/256G
    Average access time

    <0.25MS
    operating temperature

    0-85°
    power consumption

    DC Input Voltage(3.3V or 5 V ± 10%)Read and write:135mA/194Ma wait:70mA
    shock

    1500G


    Application
    the Laptop, pc, server,workstation,portable media player,digital collection apparatus and any computer equipment which need consecutive read and write speed and high reliability storage.
    Reply
  • jay401 - Wednesday, March 18, 2009 - link

    yeah, he wants "more expensive than" or "too expensive for". Reply
  • Spoelie - Wednesday, March 18, 2009 - link

    Second page as well:

    missing charts before and after this paragraph:

    "The chart above shows how much faster these affordable MLC SSDs were than the fastest 3.5” hard drive in sequential transfers. But now look at random write performance:"
    Reply
  • Spoelie - Wednesday, March 18, 2009 - link

    chart 1 on page 2 now shows sequential read but the paragraph is changed to mention random read ;)

    page 21: As far as I know, this is THE one of THE only reviews

    Some very surprising benchmark results for the ocz vertex, I thought the new firmware tanked sequential read speeds (to 80-90) based on the explanation beforehand, but not according to the actual graphs.
    Reply
  • Spoelie - Wednesday, March 18, 2009 - link

    third page, first table, first column: SSD and HDD entries are switched Reply
  • mikaela - Tuesday, March 16, 2010 - link

    yeah great info. also great resource Reply

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