What is the fastest way to create a checksum for large files in C#

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The problem here is that SHA256Managed reads 4096 bytes at a time (inherit from FileStream and override Read(byte[], int, int) to see how much it reads from the filestream), which is too small a buffer for disk IO.

To speed things up (2 minutes for hashing 2 Gb file on my machine with SHA256, 1 minute for MD5) wrap FileStream in BufferedStream and set reasonably-sized buffer size (I tried with ~1 Mb buffer):

// Not sure if BufferedStream should be wrapped in using block
using(var stream = new BufferedStream(File.OpenRead(filePath), 1200000))
{
    // The rest remains the same
}

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