Hashing first 100MB of a file

gistfile1.cs

//Grab a SHA1 of the first 100MB file
LogToolbox.TraceMessage(string.Format("{0}: Generating SHA1: {1}", m_Parent.CMName, file.Key));
using (HashAlgorithm sha = new SHA1CryptoServiceProvider())
{
    FileStream fs = null;
    try
    {
        int bytesToSHA = 1024 * 1024 * 100; //100MB
        byte[] first100MB = new byte[bytesToSHA];
        fs = new FileStream(file.Key, FileMode.Open, FileAccess.Read);
        if (info.FileSize < bytesToSHA)
        {
            fs.Read(first100MB, 0, (int)info.FileSize);
        }
        else
        {
            fs.Read(first100MB, 0, bytesToSHA);
        }
        info.SHA1 = BitConverter.ToString(sha.ComputeHash(first100MB)).Replace("-", "");
    }
    catch (Exception ex)
    {
        LogToolbox.TraceMessage(string.Format("{0} SHA 1 Generation failed for{1} - {2}", m_Parent.CMName, file.Key, ex.Message));
    }
    finally
    {
        if (fs != null)
        {
            fs.Close();
            fs.Dispose();
        }
    }
}