SFTP File transfer performance using Paramiko vs Asyncssh

Question

I am comparing 2 different methods to download files from a sftp server.

1. Using Paramiko.Transport(), adjusting the buffer size and downloading the file in chunks

2. Using Asyncssh, also adjusting the buffer size and downloading the file in chunks

Downloading 2 files took:

1. Paramiko = 119 seconds
2. Asyncssh = 123 seconds

Downloading 4 files took:

1. Paramiko = 217 seconds
2. Asyncssh = 231 seconds

I would assume as the file number increase async will perform much better compared to sequentially downloading the file. However, the results are the same or even worst.

Why is this possible? And is there a faster method to perform similar functionalities?

Paramiko Code

def create_sftp_client(host, port, username, password):
    transport = paramiko.Transport((host, port))
    transport.connect(username=username, password=password)
    
    # Increase buffer size
    transport.default_window_size = 2**40 - 1
    transport.packetizer.REKEY_BYTES = 2**50
    transport.packetizer.REKEY_PACKETS = 2**50
    
    return paramiko.SFTPClient.from_transport(transport)

def download_file(sftp, remote_path, local_path, chunk_size=1024 * 1024 * 10):
    with sftp.file(remote_path, 'r') as remote_file, open(local_path, 'wb') as local_file:
        remote_file.prefetch()
        while True:
            data = remote_file.read(chunk_size)
            if not data:
                break
            local_file.write(data)
            print(f"Downloading {remote_path}: {local_file.tell()} bytes transferred")

def download_dir(sftp, remote_dir, local_dir):
    if not os.path.exists(local_dir):
        os.makedirs(local_dir)
    for item in sftp.listdir_attr(remote_dir):
        remote_path = os.path.join(remote_dir, item.filename)
        local_path = os.path.join(local_dir, item.filename)
        if item.st_mode & 0o40000:  # Check if it's a directory
            download_dir(sftp, remote_path, local_path)
        else:
            download_file(sftp, remote_path, local_path)

def file_download(host, port, username, password, local_dir, remote_dir):
    try:
        sftp = create_sftp_client(host, port, username, password)
        download_dir(sftp, remote_dir, local_dir)
        sftp.close()
    except FileNotFoundError:
        print(f"File not found: {remote_dir}")

AsyncSSH code

async def create_sftp_client(host, port, username, password):
    conn = await asyncssh.connect(host, port=port, username=username, password=password, known_hosts=None)
    return await conn.start_sftp_client()

async def download_file(sftp, remote_path, local_path, chunk_size=1024 * 1024 * 10):
    try:
        async with sftp.open(remote_path, 'rb') as remote_file, aiofiles.open(local_path, 'wb') as local_file:
            while True:
                data = await remote_file.read(chunk_size)
                if not data:
                    break
                await local_file.write(data)
                print(f"Downloading {remote_path}: {local_file.tell()} bytes transferred")
    except Exception as e:
        print(f"Error downloading {remote_path}: {e}")

async def download_dir(sftp, remote_dir, local_dir):
    if not os.path.exists(local_dir):
        os.makedirs(local_dir)
    
    tasks = []
    for item in await sftp.listdir(remote_dir):
        remote_path = os.path.join(remote_dir, item)
        local_path = os.path.join(local_dir, item)
        stat = await sftp.stat(remote_path)
        if stat.permissions & 0o40000:  # Check if it's a directory
            tasks.append(download_dir(sftp, remote_path, local_path))
        else:
            tasks.append(download_file(sftp, remote_path, local_path))
    
    await asyncio.gather(*tasks)

async def file_download(host, port, username, password, local_dir, remote_dir):
    try:
        sftp = await create_sftp_client(host, port, username, password)
        await download_dir(sftp, remote_dir, local_dir)
    except FileNotFoundError:
        print(f"File not found: {remote_dir}")
    except Exception as e:
        print(f"Error: {e}")