stat to get filesize is a pathlogically bad pattern on Windows. If I remove the call to fileSize() in kvtest and instead replace it with 16k (since the max size in the post is 12k), I can significantly improve the time measured on Windows 10.

Before:

  C:\temp>kvtest run test1.dir --count 100k --blob-api 
  --count 100000 --max-id 1000 --asc
  Total elapsed time: 9.495
  Microseconds per BLOB read: 94.950
  Content read rate: 104.0 MB/s

After:

  C:\temp>kvtest run test1.dir --count 100k --blob-api
  --count 100000 --max-id 1000 --asc
  Total elapsed time: 5.218
  Microseconds per BLOB read: 52.180
  Content read rate: 313.3 MB/s

showing here the stable-ish numbers after a couple of runs of each version to let the cache warm up.

Windows is a completely different beast than Unix and you need to know the beast to tame it.

You might say that stat+open+read+close should be compared/measured together. In that case my answer would be that you would not read all files in a directory in this way on Windows anyway. You'd use overlapped I/O with buffers of FS cache granularity (which is 64Kb, unless it has changed in recent versions of Windows). It wouldn't matter for smaller files anyway (since the OS aggressively reads ahead when you open a file) and would be better for larger files.

It is a bugbear of mine when I see complaints about Windows from people who never actually tried to optimize for the OS.

reading blobs in Sqlite from db is still ~3x faster on my Surface Pro 2017 (don't call it Surface Pro 5!), but that's to be expected.