Filling up SSD's

Discussion in 'SSD and HDD storage' started by heymian, May 7, 2016.

  1. heymian

    heymian Master Guru

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    I was reading this article that states write performance significantly drops as you fill up a SSD drive. The article recommends leaving 25% of your drive space free.

    I have a Neutron GTX 240GB (223GB available) as a secondary SSD. So according to the article, I should leave 55.75 GB free. Sounds kind of ridiculous.
     
  2. Extraordinary

    Extraordinary Ancient Guru

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    This explains it pretty well

    Empty Blocks and Partially Filled Blocks


    NAND Flash memory writes data in 4 KB pages inside of 256 KB blocks. To add additional pages to a partially filled block, the solid-state drive must erase the entire block before writing data back to it.

    As your solid-state drive fills up, fewer and fewer empty blocks are available. In their place are partially filled blocks. The solid-state drive can’t just write the new data to these partially filled blocks — that would erase the existing data. Instead of a simple write operation, the solid-state drive has to read the value of the block into its cache, modify the value with the new data, and then write it back. Bear in mind that writing a file will likely involve writing to many blocks, so this can introduce a significant amount of additional delay.



    TRIM Doesn’t Consolidate Partially Filled Blocks

    If you fill a drive to capacity or near capacity, it’s likely that you’ll end up with many partially filled blocks after you delete files. The TRIM command just directs a solid-state drive to remove file data when the file is deleted. It doesn’t force the drive to do any sort of cleanup operation.
    In other words, fill a solid-state drive to capacity before deleting files and you’ll likely end up with many partially filled blocks. The drive won’t go out of its way to consolidate these partially-filled blocks into full blocks, freeing up empty blocks. The drive will still be full of partially filled blocks and write performance will be degraded.



    http://www.howtogeek.com/165542/why-solid-state-drives-slow-down-as-you-fill-them-up/
     

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