I have two SSD disks of 256GB and I want to create a single spanning volume of 512GB. I am using Windows 10. What I want to know is how will Windows handle this under the hood.

Will the first disk fill up before the second one starts being used, or will Windows use both disks. For example, if I have 256GB of data on the spanning volume, will it be divided to 128GB on first and 128GB on second physical disk or will it all be on the first disk with the second disk empty? Would this behavior be any different if I were using two HDDs?

  • 1
    Data is not "spread" across the disks in a spanned volume. Data is written to the first disk in the volume and then when that disk is full data is written to the next disk, and so on. It's no different whether the disks are SSD's or typical HDD's.
    – joeqwerty
    Nov 12, 2015 at 15:02
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    Possible duplicate of Spanning volume disk usage
    – testing
    Feb 17, 2016 at 16:54
  • @testing I think the possible duplicate goes in the opposite direction. Because this question is the only one of Igor Ševo's two duplicate questions that has an accepted answer, I think this question should be left open.
    – karel
    Feb 22, 2016 at 4:02
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    @karel: Is it possible to merge those two threads? E.g. to take the answer from the other thread and insert it here? I flagged the other one because it was posted earlier, but I also think the one with the accepted answer should stay open.
    – testing
    Feb 22, 2016 at 8:40

2 Answers 2


Depending on how you decide to configure Windows Storage Spaces, you can either stripe data across all devices in the pool, or use standard mirroring, or even RAID 3.

See this site for details.

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With no RAID controller, and only doing Windows Dynamic Volumes,the answer to how it's handled is in part answered by how you configure the volume: You can make it stripe (the key feature of RAID 0) or concatenate (fill one then the other).

If you have a RAID controller you can configure a RAID-0 to stripe across both drives and Windows 10 will consider it a single drive presented by the RAID controller. In this case, the drives fill up at the same rate, each containing half of every file you write to the RAID, and (the main benefit for RAID-0s) this scenario will give you approximately double the read and write speeds of a single drive.

Some details and questions (some because you're talking SSDs):

  • Do you actually have a RAID controller? It's dedicated to making this as transparent as possible to Windows.
  • Do you particularly value SSD longevity (they live longer than most users' needs)?
  • If yes, does Windows 10 include support for TRIM or other SSD longevity techniques in Dynamic Volumes (Windows 7 did not)? I don't have this answer.
  • Does your hypothetical RAID chipset and the drivers for it support TRIM?
  • Doubling read and write speeds of SSDs is "most important"? I can imagine that only for a high performance file server which never processes data other than sending and receiving. If any actual processing takes place, I have doubts that the difference is of much relevance, unless the SSDs are super slow. -- BTW, the Q is about how Windows 10 will handle this under the hood, not how a RAID solution would handle it.
    – Run CMD
    Nov 12, 2015 at 11:41
  • The answer is useful, however, as @ClassStacker pointed out, it does not answer in which way Windows 10 handles spanning volumes.
    – Igor Ševo
    Nov 12, 2015 at 12:22
  • This is the elegant part: Windows 10 would ignore it entirely and just write to the presented RAID. I'll add a bit about another option with spanned volumes allowing striping.
    – Tim G
    Nov 12, 2015 at 17:04

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