diff --git a/jeepyb/cmd/run_mirror.py b/jeepyb/cmd/run_mirror.py
index d96a763..755d72b 100644
--- a/jeepyb/cmd/run_mirror.py
+++ b/jeepyb/cmd/run_mirror.py
@@ -1,5 +1,6 @@
 #! /usr/bin/env python
 # Copyright (C) 2011 OpenStack, LLC.
+# Copyright (c) 2013 Hewlett-Packard Development Company, L.P.
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -15,73 +16,145 @@
 
 # run_mirrors reads a project config file called projects.yaml
 # It should look like:
-
+#
 # - project: PROJECT_NAME
+#
+# The algorithm it attempts to follow is:
+#
+# for each project in projects.yaml:
+#   clone if necessary and fetch origin
+#   for each project-branch:
+#     create new virtualenv
+#     pip install reqs into virtualenv
+#     if installation succeeds:
+#       pip freeze > full-reqs
+#       create new virtualenv
+#       pip install (download only) full-reqs into virtualenv
+#
+# By default only summary information is printed on stdout, but if
+# DEFAULT is enabled in the calling environment then stdout of all
+# shell commands run is also printed. Due to its copiousness and
+# buffering, however, DEBUG level output is best suited to file
+# redirection.
+#
+# If "pip install" for a branch's requirements fails to complete
+# (based on parsing of its output), that output will be copied to
+# stderr and the script will skip ahead to the next branch. This
+# makes it suitable for running in a cron job with only stdout
+# redirected to a log, and also avoids one broken project preventing
+# caching of requirements for others.
 
-import logging
 import os
 import subprocess
 import shlex
+import shutil
+import sys
+import tempfile
 import yaml
 
 
-def run_command(cmd, status=False, env={}):
+def run_command(cmd):
     cmd_list = shlex.split(str(cmd))
-    newenv = os.environ
-    newenv.update(env)
     p = subprocess.Popen(cmd_list, stdout=subprocess.PIPE,
-                         stderr=subprocess.STDOUT, env=newenv)
+                         stderr=subprocess.STDOUT)
     (out, nothing) = p.communicate()
-    if status:
-        return (p.returncode, out.strip())
     return out.strip()
 
 
-def run_command_status(cmd, env={}):
-    return run_command(cmd, True, env)
-
-
 def main():
 
-    logging.basicConfig(level=logging.ERROR)
-
+    DEBUG = True if os.environ.get('DEBUG', '').lower() in ('enabled',
+                                                            'enable',
+                                                            'true',
+                                                            'yes',
+                                                            'on',
+                                                            '1') else False
     PROJECTS_YAML = os.environ.get('PROJECTS_YAML',
                                    '/etc/openstackci/projects.yaml')
     PIP_TEMP_DOWNLOAD = os.environ.get('PIP_TEMP_DOWNLOAD',
                                        '/var/lib/pip-download')
+    PIP_DOWNLOAD_CACHE = os.environ.get('PIP_DOWNLOAD_CACHE',
+                                        '/var/cache/pip')
     GIT_SOURCE = os.environ.get('GIT_SOURCE', 'https://github.com')
-    pip_command = '/usr/local/bin/pip install -M -U -I --exists-action=w ' \
-                  '--no-install %s'
-
-    run_command(pip_command % "pip")
+    pip_format = "%s install -M -U %s --exists-action=w -b %s -r %s"
+    venv_format = ("/usr/local/bin/virtualenv --clear --distribute "
+                   "--extra-search-dir=%s %s")
 
     (defaults, config) = [config for config in
                           yaml.load_all(open(PROJECTS_YAML))]
 
+    workdir = tempfile.mkdtemp()
+    reqs = os.path.join(workdir, "reqs")
+    venv = os.path.join(workdir, "venv")
+    pip = os.path.join(venv, "bin", "pip")
+
     for section in config:
         project = section['project']
+        if DEBUG:
+            print("*********************\nupdating %s repository" % project)
 
         os.chdir(PIP_TEMP_DOWNLOAD)
         short_project = project.split('/')[1]
         if not os.path.isdir(short_project):
-            run_command("git clone %s/%s.git %s" % (GIT_SOURCE, project,
-                                                    short_project))
+            out = run_command("git clone %s/%s.git %s" % (GIT_SOURCE, project,
+                                                          short_project))
+            if DEBUG:
+                print(out)
         os.chdir(short_project)
-        run_command("git fetch origin")
+        out = run_command("git fetch origin")
+        if DEBUG:
+            print(out)
 
         for branch in run_command("git branch -a").split("\n"):
             branch = branch.strip()
             if (not branch.startswith("remotes/origin")
                     or "origin/HEAD" in branch):
                 continue
-            run_command("git reset --hard %s" % branch)
-            run_command("git clean -x -f -d -q")
             print("*********************")
             print("Fetching pip requires for %s:%s" % (project, branch))
+            out = run_command("git reset --hard %s" % branch)
+            if DEBUG:
+                print(out)
+            out = run_command("git clean -x -f -d -q")
+            if DEBUG:
+                print(out)
+            reqlist = []
             for requires_file in ("requirements.txt",
                                   "test-requirements.txt",
                                   "tools/pip-requires",
                                   "tools/test-requires"):
                 if os.path.exists(requires_file):
-                    stanza = "-r %s" % requires_file
-                    run_command(pip_command % stanza)
+                    reqlist.append(requires_file)
+            if reqlist:
+                out = run_command(venv_format % (PIP_DOWNLOAD_CACHE, venv))
+                if DEBUG:
+                    print(out)
+                out = run_command(pip_format % (pip, "", PIP_DOWNLOAD_CACHE,
+                                                " -r ".join(reqlist)))
+                if DEBUG:
+                    print(out)
+                if "\nSuccessfully installed " not in out:
+                    sys.stderr.write(out)
+                    print("pip install did not indicate success")
+                else:
+                    freeze = run_command("%s freeze -l" % pip)
+                    reqfd = open(reqs, "w")
+                    for line in freeze.split("\n"):
+                        if "==" in line:
+                            reqfd.write(line + "\n")
+                    reqfd.close()
+                    out = run_command(venv_format % (PIP_DOWNLOAD_CACHE, venv))
+                    if DEBUG:
+                        print(out)
+                    out = run_command(pip_format % (pip, "--no-install",
+                                      PIP_DOWNLOAD_CACHE, reqs))
+                    if DEBUG:
+                        print(out)
+                    if "\nSuccessfully installed " not in out:
+                        sys.stderr.write(out)
+                        print("pip install did not indicate success")
+                    print("cached:\n%s" % freeze)
+            else:
+                print("no requirements")
+
+    shutil.rmtree(workdir)