Read performance dropped in Tiered Storage Space for Win10 2004 and 20H2 RRS feed

  • Question

  • Hello,

    I just wanted to report that there is a major bug in Win10 regarding Storage Spaces.

    The following Windows versions are affected:

    Win10 2004

    Win10 20H2

    Older windows versions have no problems.


    I have tested a Tiered Storage Space with one SSD and one HDD.

    File system is ReFS, so the newer tiering mechanism is used where each file access goes over the SSD. Also read access on files that are currently on the HDD should be transferred on the SSD first and afterwards be used from the SSD by Storage Spaces. It seems that Microsoft has broken this. At least this was the behavior before v2004.

    BTW, this config can be created with Win10 Enterprise and the power shell.

    I was testing the disk performance with CrystalDiskMark 6.0.2 x64. 

    Before the update I had a performance of about:

    4KiB Q8T8 of about 100 MB/s

    After the update it has dropped to:

    4KiB Q8T8 lower than 1 MB/s

    Similar for the other 4KiB tests.

    Q32T1 and whole write performance is still the same after the update. Only 4k file reads are affected.

    The bottom line is that Win10 2004 and Win10 20H2 is unusable with tiered storage spaces and ReFS. I had to run virtual machines from such a disk and they are totally unusable with this weak read performance.

    If you revert Win10 2004 and Win10 20H2 then everything works again.

    Microsoft, please fix this issue. On 2004 I was hoping that you will fix this in the next version but now 20H2 arrived with the same problem.

    Thank you.

    Monday, November 9, 2020 7:57 AM