SSD Capacity v Speed

Discussion in 'Buying Tips and Advice' started by greenmountain, May 22, 2011.

  1. greenmountain macrumors newbie

    Jul 7, 2010
    I know that conventional HDD's suffer a significant loss in speed/performance once they pass 75 or 80% of capacity. Is the same true for SSD's?

    Thanks in advance for any advice the forum can offer.
  2. MartyMacLord macrumors newbie

    Apr 26, 2011

    Most of the ssd's are disingned to maintain there speed. But if you don't use the TRIM command ssd's gros slow over time. However some ssd's do use a internal trim command (or something like that) and don't get slow over time.
  3. greenmountain thread starter macrumors newbie

    Jul 7, 2010
    Yes, I have read that SSD performance deteriorates over time. My question, however, is not about age but rather about filling up the disk. If you take a brand-new HDD and immediately fill it to, say, 85% of capacity it immediately slows down. A lot. Would the same thing happen with a brand-new SSD? Or do they retain their speed more or less regardless of how full they are? If filling the disk with data does slow it down, where is the tipping point? 60%? 75%? 90%?

  4. zhenya macrumors 603


    Jan 6, 2005
    Modern SSD's all use some percentage of their capacity as reserved 'spare' area to allow them to keep up performance. However, when any drive gets very full, you will start to see slowdowns - but this is operating system related - and has nothing to do with the physical hardware. The OS needs a certain amount of space to write data to the disk - even with a lot of RAM. If you allow it to get entirely full, things are going to slow down.
  5. SimonTheSoundMa macrumors 6502a

    Aug 6, 2006
    Birmingham, UK
    OS X on mechanical drives slows down when the drive is mostly full over time because files start to become fragmented and files become scattered. OS X keeps similar files near to each other, even has a hot zone near to the outside of the platters where throughput is faster for frequently accessed files, which all reducing seek time, when it gets full it switches this mechanism off as there isn't enough free space.

    This doesn't matter with SSDs. The OS does not know where the files are located so file fragmentation and scattering cannot be managed. Seek time is almost zero and there are no outer tracks that have a different throughput so doesn't matter. Files can be stored anywhere on the drive and fragmentation doesn't matter.

    As for TRIM, some of the new controllers such as Sandforce do not use TRIM, they do it in hardware.

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