How to get max allowed filesize in .Net?

Question

Hello there,

Does anyone know how to (natively) get the max allowed file size for a given drive/folder/directory? As in for Fat16 it is ~2gb, Fat32 it was 4gb as far as I remember and for the newer NTFS versions it is something way beyond that.. let alone Mono and the underlying OSes.

Is there anything I can read out / retrieve that might give me a hint on that? Basically I -know- may app will produce bigger, single files than 2gb and I want to check for that when the user sets the corresponding output path(s)...

Cheers & thanks, -J

Answer 1

How about using System.Info.DriveInfo.DriveFormat to retrieve the drive's file system (NTFS, FAT, ect.)? That ought to give you at least some idea of the supported file sizes.

Answer 2

This may not be the ideal solution, but I will suggest the following anyway:

// Returns the maximum file size in bytes on the filesystem type of the specified drive.
long GetMaximumFileSize(string drive)
{
    var driveInfo = new System.IO.DriveInfo(drive)

    switch(driveInfo.DriveFormat)
    {
        case "FAT16":
            return 1000; // replace with actual limit
        case "FAT32":
            return 1000; // replace with actual limit
        case "NTFS":
            return 1000; // replace with actual limit
    }
}

// Examples:
var maxFileSize1 = GetMaximumFileSize("C"); // for the C drive
var maxFileSize2 = GetMaximumFileSize(absolutePath.Substring(0, 1)); // for whichever drive the given absolute path refers to

This page on Wikipedia contains a pretty comprehensive list of the maximum file sizes for various filesystems. Depending on the number of filesystems for which you want to check in the GetMaximumFileSize function, you may want to use a Dictionary object or even a simple data file rather than a switch statement.

Now, you may be retrieve the maximum file size directly using WMI or perhaps even the Windows API, but these solutions will of course only be compatible with Windows (i.e. no luck with Mono/Linux). However, I would consider this a reasonably nice purely managed solution, despite the use of a lookup table, and has the bonus of working reliably on all OSs.

Hope that helps.