Creating a fixed size disk requires 'extra space' in the underlying stream

[Yazwh0]

Take the code below, if the - 512 isn't included you get a System.NotSupportedException: 'Memory stream is not expandable.'

Presumably this is for the VHD footer?

using DiscUtils.Fat;
using DiscUtils.Partitions;
using DiscUtils.Vhd;

// create disk
{
    var size = 32 * 1024 * 1024;
    var rawMemory = new byte[size];
    var data = new MemoryStream(rawMemory, 0, size, true);

    var disk = Disk.InitializeFixed(data, DiscUtils.Streams.Ownership.None, (long)size - 512); // needed for the vhd footer??
    BiosPartitionTable.Initialize(disk, WellKnownPartitionType.WindowsFat);
    var fileSystem = FatFileSystem.FormatPartition(disk, 0, "TEST");

    Console.WriteLine($"Is : {fileSystem.FatVariant}");

    var newFile = fileSystem.OpenFile("FOO.TXT", FileMode.CreateNew, FileAccess.Write);
    newFile.Write(new byte[] { 1, 2, 3, 4 });
    newFile.Close();

    Console.WriteLine($"File exists? {fileSystem.Exists("FOO.TXT")}");

    File.WriteAllBytes(@"c:\temp\test.vhd", rawMemory);
}

[LTRData]

Yes, most disk image formats need space for metadata and they also need to be aligned to a certain block size.