File path = Environment.getExternalStorageDirectory();
    /*
     * Retrieve overall information about the space on a filesystem. 
     * This is a wrapper for Unix statvfs(). 
     */
    StatFs stat = new StatFs(path.getPath());
    long blockSize = stat.getBlockSize();
    long totalBlocks = stat.getBlockCount();
    long availableBlocks = stat.getAvailableBlocks();
    
    long totalSize = blockSize * totalBlocks;
    long availSize = availableBlocks * blockSize;
    
    String totalStr = Formatter.formatFileSize(this, totalSize);
    String availStr = Formatter.formatFileSize(this, availSize);