diff --git a/blobsend/__init__.py b/blobsend/__init__.py
index 7b2936e..1e46e51 100644
--- a/blobsend/__init__.py
+++ b/blobsend/__init__.py
@@ -1,10 +1,59 @@
 import hashlib
+from threading import Semaphore
 
 
 CHUNK_SIZE = 1024 * 1024 * 4  # 4 mb chunks
 
 
 def hash_chunk(data):
-    h = hashlib.md5()
+    h = hashlib.sha256()
     h.update(data)
     return h.hexdigest()
+
+
+class FilePool(object):
+    def __init__(self, instances, open_function):
+        """
+        Pool of many files handle
+        """
+        self.instances = [open_function() for i in range(0, instances)]
+        self.lock = Semaphore(instances)
+
+    def get(self):
+        """
+        Return a context-manager that contains the file object
+        """
+        return FilePoolSlice(self)
+
+    def close(self):
+        for f in self.instances:
+            f.close()
+
+    def _get_locked(self):
+        """
+        Acquire and return an instance from the pool
+        """
+        self.lock.acquire()
+        return self.instances.pop()
+
+    def _return_locked(self, instance):
+        """
+        Release an instance emitted by get_locked
+        """
+        self.instances.append(instance)
+        self.lock.release()
+
+
+class FilePoolSlice(object):
+    def __init__(self, pool):
+        self.pool = pool
+        self.mine = None
+
+    def __enter__(self):
+        #TODO don't use me more than once
+        self.mine = self.pool._get_locked()
+        self.mine.seek(0)
+        return self.mine
+
+    def __exit__(self, exc_type, exc_value, exc_traceback):
+        self.pool._return_locked(self.mine)
diff --git a/blobsend/cli.py b/blobsend/cli.py
index 7dd2ebe..eb0ae47 100644
--- a/blobsend/cli.py
+++ b/blobsend/cli.py
@@ -1,13 +1,18 @@
 import argparse
 from urllib.parse import urlparse
+from concurrent.futures import ThreadPoolExecutor
 from blobsend import CHUNK_SIZE
 from blobsend.client_file import FileChunkClient
+# from blobsend.client_basic_file import FileChunkClient
 from blobsend.client_ssh import SshChunkClient
+# from blobsend.client_ssh import SshChunkClientOld as SshChunkClient
+from blobsend.client_ssh import SshChunkClientParallelConnections
 
 
 SCHEMES = {
     "file": FileChunkClient,
     "ssh": SshChunkClient,
+    "pssh": SshChunkClientParallelConnections,
 }
 
 
@@ -24,13 +29,7 @@ def get_args():
     return parser.parse_args(), parser
 
 
-def main():
-    args, parser = get_args()
-    print(args)
-
-    src = get_client(urlparse(args.src), True)
-    dest = get_client(urlparse(args.dest), False)
-
+def send(src, dest):
     num_chunks = src.get_length() // CHUNK_SIZE
 
     dest_hashes_iter = dest.get_hashes()
@@ -52,6 +51,50 @@ def main():
 
     dest.set_length(src.get_length())
 
+
+def send_parallel(src, dest):
+    num_chunks = src.get_length() // CHUNK_SIZE
+
+    dest_hashes_iter = dest.get_hashes()
+
+    def copy_chunk(chunk_number):
+        print("Copying chunk", chunk_number, "/", num_chunks)
+        blob = src.get_chunk(chunk_number)
+        dest.put_chunk(chunk_number, blob)
+
+    with ThreadPoolExecutor(max_workers=10) as pool:
+        futures = []
+        for src_chunk_number, src_chunk_hash in src.get_hashes():
+            dest_chunk_number = None
+            dest_chunk_hash = None
+            try:
+                dest_chunk_number, dest_chunk_hash = next(dest_hashes_iter)
+            except StopIteration:
+                pass
+
+            if dest_chunk_number is not None and src_chunk_number != dest_chunk_number:
+                raise Exception("sequence mismatch?")
+
+            # print("chunk", src_chunk_number, src_chunk_hash, "vs", dest_chunk_hash)
+
+            if src_chunk_hash != dest_chunk_hash:
+                futures.append(pool.submit(copy_chunk, src_chunk_number))
+        for f in futures:
+            f.result()
+
+    dest.set_length(src.get_length())
+
+
+def main():
+    args, parser = get_args()
+    print(args)
+
+    src = get_client(urlparse(args.src), True)
+    dest = get_client(urlparse(args.dest), False)
+
+    # send(src, dest)
+    send_parallel(src, dest)
+
     src.close()
     dest.close()
 
diff --git a/blobsend/client_file.py b/blobsend/client_file.py
index 7cfa802..9307f04 100644
--- a/blobsend/client_file.py
+++ b/blobsend/client_file.py
@@ -1,18 +1,27 @@
 import os
 from blobsend.client_base import BaseChunkClient
-from blobsend import CHUNK_SIZE, hash_chunk
+from blobsend import CHUNK_SIZE, hash_chunk, FilePool
 
 
 class FileChunkClient(BaseChunkClient):
-    def __init__(self, fpath, chunk_size=CHUNK_SIZE):
+    def __init__(self, fpath, is_src, chunk_size=CHUNK_SIZE):
         super().__init__(chunk_size)
         self.fpath = fpath
-        self.file = open(self.fpath, "ab+")  # for get chunk operations, this generic file is used instead of doing lots of open/close
-        self.file.seek(0)
+
+        if not is_src and not os.path.exists(self.fpath):
+            with open(self.fpath, "wb"):
+                pass
+
+        def _fpool_open():
+            f = open(self.fpath, "rb+")  # for get chunk operations, this generic file is used instead of doing lots of open/close
+            f.seek(0)
+            return f
+
+        self.fpool = FilePool(10, _fpool_open)
 
     def get_hashes(self):
         i = 0
-        with open(self.fpath, "rb+") as f:
+        with self.fpool.get() as f:
             while True:
                 data = f.read(self.chunk_size)
                 if not data:
@@ -27,8 +36,9 @@ class FileChunkClient(BaseChunkClient):
         position = chunk_number * self.chunk_size
         if position > os.path.getsize(self.fpath):#TODO not sure if > or >=
             raise Exception("requested chunk {} is beyond EOF".format(chunk_number))
-        self.file.seek(position)#TODO not thread safe
-        return self.file.read(self.chunk_size)
+        with self.fpool.get() as f:
+            f.seek(position)#TODO not thread safe
+            return f.read(self.chunk_size)
 
     def put_chunk(self, chunk_number, contents):
         """
@@ -43,21 +53,23 @@ class FileChunkClient(BaseChunkClient):
         """
         get the file size
         """
-        self.file.seek(0, 2)  # seek to end
-        return self.file.tell()
+        with self.fpool.get() as f:
+            f.seek(0, 2)  # seek to end
+            return f.tell()
 
     def set_length(self, length):
         if length < self.get_length():
-            self.file.truncate(length)
+            with self.fpool.get() as f:
+                f.truncate(length)
         # do nothing for the case of extending the file
         # put_chunk handles it
 
     def close(self):
-        self.file.close()
+        self.fpool.close()
 
     @staticmethod
     def from_uri(uri, is_src):
         """
         instantiate a client from the given uri
         """
-        return FileChunkClient(uri.path)
+        return FileChunkClient(uri.path, is_src)
diff --git a/blobsend/client_ssh.py b/blobsend/client_ssh.py
index c456e48..7a8f2da 100644
--- a/blobsend/client_ssh.py
+++ b/blobsend/client_ssh.py
@@ -1,6 +1,6 @@
 import paramiko
 from blobsend.client_base import BaseChunkClient
-from blobsend import CHUNK_SIZE, hash_chunk
+from blobsend import CHUNK_SIZE, hash_chunk, FilePool
 
 
 """
@@ -12,6 +12,164 @@ REMOTE_UTILITY = "/Users/dave/code/blobsend/testenv/bin/_blobsend_ssh_remote"#
 
 
 class SshChunkClient(BaseChunkClient):
+    def __init__(self, server, username, password, fpath, is_src, chunk_size=CHUNK_SIZE):
+        super().__init__(chunk_size)
+        self.fpath = fpath
+        self.ssh = paramiko.SSHClient()
+        self.ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
+        self.ssh.connect(hostname=server,
+                         username=username,
+                         password=password)
+
+        self.sftp = self.ssh.open_sftp()
+
+        # If the file doesnt exist and we are the destination, create it
+        if not is_src:
+            try:
+                with self.sftp.open(self.fpath, "r"):
+                    pass
+            except FileNotFoundError:
+                with self.sftp.open(self.fpath, "wb"):
+                    pass
+
+        def _fpool_open():
+            sftp = self.ssh.open_sftp()
+            f = sftp.open(self.fpath, "r+")
+            f.seek(0)
+            return f
+
+        self.fpool = FilePool(8, _fpool_open)
+
+    def get_hashes(self):
+        stdin, stdout, stderr = self.ssh.exec_command("{} chunks {}".format(REMOTE_UTILITY, self.fpath))#TODO safe arg escapes
+        stdin.close()
+        for line in iter(lambda: stdout.readline(1024), ""):
+            chunk_number, chunk_hash = line.strip().split(" ")
+            yield (int(chunk_number), chunk_hash, )
+        exit = stdout.channel.recv_exit_status()
+        if exit != 0:
+            raise Exception("hash command exit code was {}: {}".format(exit, stderr.read()))
+
+    def get_chunk(self, chunk_number):
+        position = chunk_number * self.chunk_size
+        if position > self.get_length():
+            raise Exception("requested chunk {} is beyond EOF".format(chunk_number))
+        with self.fpool.get() as f:
+            f.seek(position)
+            return f.read(self.chunk_size)
+
+    def put_chunk(self, chunk_number, contents):
+        position = chunk_number * self.chunk_size
+        with self.fpool.get() as f:
+            f.seek(position)
+            f.write(contents)
+
+    def get_length(self):
+        with self.fpool.get() as f:
+            f.seek(0, 2)  # seek to end
+            return f.tell()
+
+    def set_length(self, length):
+        if length < self.get_length():
+            with self.fpool.get() as f:
+                f.truncate(length)
+        # do nothing for the case of extending the file
+        # put_chunk handles it
+
+    def close(self):
+        self.fpool.close()
+
+    @staticmethod
+    def from_uri(uri, is_src):
+        """
+        instantiate a client from the given uri
+        """
+        return SshChunkClient(uri.hostname, uri.username, uri.password, uri.path, is_src)
+
+
+class SshChunkClientParallelConnections(BaseChunkClient):
+    def __init__(self, server, username, password, fpath, is_src, chunk_size=CHUNK_SIZE):
+        super().__init__(chunk_size)
+        self.fpath = fpath
+        self.ssh = paramiko.SSHClient()
+        self.ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
+        self.ssh.connect(hostname=server,
+                         username=username,
+                         password=password)
+
+        self.sftp = self.ssh.open_sftp()
+
+        # If the file doesnt exist and we are the destination, create it
+        if not is_src:
+            try:
+                with self.sftp.open(self.fpath, "r"):
+                    pass
+            except FileNotFoundError:
+                with self.sftp.open(self.fpath, "wb"):
+                    pass
+
+        def _fpool_open():
+            ssh = paramiko.SSHClient()
+            ssh.set_missing_host_key_policy(paramiko.AutoAddPolicy())
+            ssh.connect(hostname=server,
+                        username=username,
+                        password=password)
+
+            sftp = ssh.open_sftp()
+            f = sftp.open(self.fpath, "r+")
+            f.seek(0)
+            return f
+
+        self.fpool = FilePool(8, _fpool_open)
+
+    def get_hashes(self):
+        stdin, stdout, stderr = self.ssh.exec_command("{} chunks {}".format(REMOTE_UTILITY, self.fpath))#TODO safe arg escapes
+        stdin.close()
+        for line in iter(lambda: stdout.readline(1024), ""):
+            chunk_number, chunk_hash = line.strip().split(" ")
+            yield (int(chunk_number), chunk_hash, )
+        exit = stdout.channel.recv_exit_status()
+        if exit != 0:
+            raise Exception("hash command exit code was {}: {}".format(exit, stderr.read()))
+
+    def get_chunk(self, chunk_number):
+        position = chunk_number * self.chunk_size
+        if position > self.get_length():
+            raise Exception("requested chunk {} is beyond EOF".format(chunk_number))
+        with self.fpool.get() as f:
+            f.seek(position)
+            return f.read(self.chunk_size)
+
+    def put_chunk(self, chunk_number, contents):
+        position = chunk_number * self.chunk_size
+        with self.fpool.get() as f:
+            f.seek(position)
+            f.write(contents)
+
+    def get_length(self):
+        with self.fpool.get() as f:
+            f.seek(0, 2)  # seek to end
+            return f.tell()
+
+    def set_length(self, length):
+        if length < self.get_length():
+            with self.fpool.get() as f:
+                f.truncate(length)
+        # do nothing for the case of extending the file
+        # put_chunk handles it
+
+    def close(self):
+        self.fpool.close()
+
+    @staticmethod
+    def from_uri(uri, is_src):
+        """
+        instantiate a client from the given uri
+        """
+        return SshChunkClientParallelConnections(uri.hostname, uri.username, uri.password, uri.path, is_src)
+
+
+class SshChunkClientOld(BaseChunkClient):
     def __init__(self, server, username, password, fpath, is_src, chunk_size=CHUNK_SIZE):
         super().__init__(chunk_size)
         self.fpath = fpath
@@ -32,8 +190,6 @@ class SshChunkClient(BaseChunkClient):
                 with self.sftp.open(self.fpath, "wb") as f:
                     pass
 
-        # it seems like mode "ab+" doesn't work the same way under paramiko
-        # it refuses to seek before the open point (which is the end of the file)
         self.file = self.sftp.open(self.fpath, "r+")
 
     def get_hashes(self):
@@ -42,6 +198,9 @@ class SshChunkClient(BaseChunkClient):
         for line in iter(lambda: stdout.readline(1024), ""):
             chunk_number, chunk_hash = line.strip().split(" ")
             yield (int(chunk_number), chunk_hash, )
+        exit = stdout.channel.recv_exit_status()
+        if exit != 0:
+            raise Exception("hash command exit code was {}: {}".format(exit, stderr.read()))
 
     def get_chunk(self, chunk_number):
         position = chunk_number * self.chunk_size
@@ -61,7 +220,8 @@ class SshChunkClient(BaseChunkClient):
 
     def set_length(self, length):
         if length < self.get_length():
-            self.file.truncate(length)
+            with self.fpool.get() as f:
+                f.truncate(length)
         # do nothing for the case of extending the file
         # put_chunk handles it
 
@@ -73,4 +233,4 @@ class SshChunkClient(BaseChunkClient):
         """
         instantiate a client from the given uri
         """
-        return SshChunkClient(uri.hostname, uri.username, uri.password, uri.path, is_src)
+        return SshChunkClientOld(uri.hostname, uri.username, uri.password, uri.path, is_src)
diff --git a/blobsend/client_ssh_remote.py b/blobsend/client_ssh_remote.py
index b6c366d..6ab798f 100644
--- a/blobsend/client_ssh_remote.py
+++ b/blobsend/client_ssh_remote.py
@@ -6,7 +6,7 @@ from blobsend.client_file import FileChunkClient
 
 
 def cmd_chunks(args, parser):
-    c = FileChunkClient(args.fpath)
+    c = FileChunkClient(args.fpath, False)
     for chunk_number, chunk_hash in c.get_hashes():
         print(chunk_number, chunk_hash)
         sys.stdout.flush()