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I've done a lot of digging to try and figure out why I am experiencing slow write speeds to my SSD drives. They’re model number is: PNY XLR8 SSD9SC240GMDA-RB 2.5" 240GB SATA III Internal Solid State Drive (SSD).

They are running on SATA ports 1 and 2 TRIM is enabled. I can’t get SMART data because they’re set up in a RAID 0 (though the problem still persists with individual drives).

  1. I've run defrag using O&O's offline defrag tool.
  2. I took my SSD drives off of RAID 0 and tested them individually with the same results.
  3. My external USB hard drive is faster at writing than my SSDs!
  4. I've made sure that my drive is set to AHCI (before, it was RAID 0)

I am using Windows 7 and these drives were running just fine before. The funny thing is that now the problem is occurring with both drives.

FWIW, I upgraded to Windows 10 a few weeks ago and started noticing the slowness. Thinking it was Windows 10 that was the cause, I downgraded back to Windows 7 Ultimate.

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Here's the AS SSD result (clearly not normal):

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    Please oh please don't defragment SSDs. Fragmentation is a problem with rotational media because of seek latency, and SSDs have practically zero seek latency. Defragmenting SSDs, in the best of cases, will have no effect whatsoever.
    – user
    Sep 1, 2015 at 19:01
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    Please edit your question to include SMART data, ideally from both drives.
    – user
    Sep 1, 2015 at 19:01
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    I also don't really see the point in making a RAID 0 from SSDs, increasing chance of data loss yet not increasing write bandwidth significantly.
    – Tetsujin
    Sep 1, 2015 at 19:10
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    You don't mention the size or capacity of your drives. I've seen reports elsewhere that performance takes a major hit once the drive gets to 70-75% full. If you have pretty full drives, you might consider clearing them off and testing again.
    – WPrecht
    Sep 1, 2015 at 19:22
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    What make and model are the SSDs? How full are they? My bet is that your write times are so slow because writes are requiring an erase operation and erases are very slow. (Making sure TRIM is enabled and forcing a manual TRIM run may help. If the disks are less than 30% free, making space may help.) Sep 1, 2015 at 20:12

1 Answer 1

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Fragmentation can occur when an SSD has less than 25% of free space left.

The reason for this is in how an SSD stores its data.

Your entire SSD is made out of clusters. Each cluster has sectors in it which can be filled with data.

When a file is written to your SSD, it will be written to a new cluster. It is done in such way that speed is guaranteed. When a file is removed, it will check if that cluster is empty and if so, it is marked as cleared. This is done by the function TRIM.

Now, the problem is, that at some point, your drive will be filled with enough data to make all available clusters filled with some data. This is not a bad thing, because most clusters will still have some empty space in them. When a new file is written it will then be stored in one or more of these clusters. It is here where your drive looses its speed. Not so much by how the file is stored, but because it has to find empty space rather than just finding the next empty cluster.

After your drive has been fragmented, and a file is deleted, the chance becomes small that the cluster that file was in, is completely empty. If the cluster is not empty, TRIM will not mark that cluster as cleared, and thus it will not be moved to the pool of free clusters.

So in order to fix this, first make sure you have at least 50% of free space on your SSD available, then find a defragmentation tool especially for SSD drives.

If you have another disk available, and the SSD is not running your OS, you can consider moving all your files from the SSD to another disk and then format your SSD. This will cause TRIM to mark all your clusters as empty and moving the data back will do so without causing fragmentation. Do note, this last move method is not necessarily better than a defragger. These defraggers will try to move as little data as possible while obtaining the goal, whereas moving all data to your other drive will essentially cause all clusters to be written from and to atleast two times.

One last note: The 25% of free space is a rule of thumb, not an actual established fact. Each drive is different, and with some drives it happens earlier, with some drives it happens later. So for convenience, make sure you always have at least 25% of free space on your SSD. So if your SSD is 240GB big, make sure you have at least 60GB of free space to avoid fragmentation.

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    Discussions of SSD and discussions of fragmentation just should not ever coincide. Because of the nature of SSDs, the IOPS, and the zero seek times, fragmentation is totally irrelevant. Humoring fragmentation as a problem is counterproductive. -1 to the answer.
    – killermist
    Dec 2, 2015 at 22:30
  • @killermist I'm sorry you feel this way, but please do some research for SSD's to learn that fragmentation really does matter. Your -1 is really unjustified.
    – LPChip
    Dec 3, 2015 at 7:52
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    Sorry to say, but the more and more I read, 4k and 8k "sectors" (which are humored/honored by 1Mb partition alignments) are all that is necessary to make SSDs "just work". "fragmentation" within a partition is "just handled" by the wear leveling controller of the device across all the actual capacity (which is often just massively under-reported).
    – killermist
    Dec 3, 2015 at 8:39
  • Fragmentation occurs at ANY amount of free space, it literally only depends on the amount and type of writes, and their parallelism.
    – analytik
    Jun 16, 2021 at 5:19
  • @analytik no, not with an SSD. SSD's will write their data to individual clusters as much as possible trying really hard to ensure that different files are not in the same cluster. It will archieve this as long as there is about 25% or more free space left. The SSD periodically executes TRIM which checks for all files deleted that previously occupied a cluster, and when such cluster is empty, it will mark that cluster as empty so it can be filled again. When an SSD gets filled up to the point where different files occupy the same cluster, the performance goes down quickly. Please research.
    – LPChip
    Jun 16, 2021 at 8:47

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