diff --git a/omnibus/files/private-chef-cookbooks/private-chef/libraries/du.rb b/omnibus/files/private-chef-cookbooks/private-chef/libraries/du.rb
new file mode 100644
index 0000000000..bb30c06625
--- /dev/null
+++ b/omnibus/files/private-chef-cookbooks/private-chef/libraries/du.rb
@@ -0,0 +1,25 @@
+require 'mixlib/shellout'
+module Du
+  # Calculate the disk space used by the given path. Requires that
+  # `du` is in our PATH.
+  #
+  # @param path [String] Path to a directory on disk
+  # @return [Integer] KB used by directory on disk
+  #
+  def self.du(path)
+    # TODO(ssd) 2017-08-18: Do we need to worry about sparse files
+    # here? If so, can we expect the --apparent-size flag to exist on
+    # all of our platforms.
+    command = Mixlib::ShellOut.new("du -sk #{path}")
+    command.run_command
+    if command.status.success?
+      command.stdout.split("\t").first.to_i
+    else
+      Chef::Log.error("du -sk #{path} failed with exit status: #{command.exitstatus}")
+      Chef::Log.error("du stderr: #{command.stderr}")
+      raise "du failed"
+    end
+  rescue Errno::ENOENT
+    raise "The du utility is not available. Unable to check disk usage"
+  end
+end
diff --git a/omnibus/files/private-chef-cookbooks/private-chef/libraries/statfs.rb b/omnibus/files/private-chef-cookbooks/private-chef/libraries/statfs.rb
new file mode 100644
index 0000000000..22da79a129
--- /dev/null
+++ b/omnibus/files/private-chef-cookbooks/private-chef/libraries/statfs.rb
@@ -0,0 +1,78 @@
+require 'ffi'
+
+class Statfs
+  #
+  # Statfs provides a simple interface to the statvfs system call.
+  # Since the statvfs struct varies a bit across platforms, this
+  # likely only works on Linux and OSX at the moment.
+  #
+  extend FFI::Library
+  ffi_lib FFI::Library::LIBC
+
+  attach_function(:statvfs, [:string, :pointer], :int)
+  attach_function(:strerror, [:int], :string)
+
+  FSBLKCNT_T = if RbConfig::CONFIG['host_os'] =~ /darwin|osx|mach/i
+                 :uint
+               else
+                 :ulong
+               end
+
+  # See http://man7.org/linux/man-pages/man2/statvfs.2.html
+  class Statvfs < FFI::Struct
+    spec = [
+            :f_bsize,   :ulong,      # Filesystem block size
+            :f_frsize,  :ulong,      # Fragement size
+            :f_blocks,  FSBLKCNT_T,  # Size of fs in f_frsize units
+            :f_bfree,   FSBLKCNT_T,  # Number of free blocks
+            :f_bavail,  FSBLKCNT_T,  # Number of free blocks for unpriviledged users
+            :f_files,   FSBLKCNT_T,  # Number of inodes
+            :f_ffree,   FSBLKCNT_T,  # Number of free inodes
+            :f_favail,  FSBLKCNT_T,  # Number of free inodes for unprivilged users
+            :f_fsid,    :ulong,      # Filesystem ID
+            :f_flag,    :ulong,      # Mount Flags
+            :f_namemax, :ulong       # Max filename length
+           ]
+
+    # Linux has this at the end of the struct and if we don't include
+    # it we end up getting a memory corruption error when th object
+    # gets GCd.
+    if RbConfig::CONFIG['host_os'] =~ /linux/i
+      spec << :f_spare
+      spec << [:int, 6]
+    end
+
+    layout(*spec)
+  end
+
+  def initialize(path)
+    @statvfs = stat(path)
+  end
+
+  #
+  # @returns [Integer] Free inodes on the given filesystem
+  #
+  def free_inodes
+    @statvfs[:f_favail]
+  end
+
+  #
+  # @returns [Integer] Free space in KB on the given filesystem
+  #
+  def free_space
+    # Since we are running as root we could report f_bfree but will
+    # stick with f_bavail since it will typically be more
+    # conservative.
+    (@statvfs[:f_frsize] * @statvfs[:f_bavail])/1024
+  end
+
+  private
+
+  def stat(path)
+    statvfs = Statvfs.new
+    if statvfs(path, statvfs.to_ptr) != 0
+      raise 'statvfs: ' + strerror(FFI.errno)
+    end
+    statvfs
+  end
+end
diff --git a/omnibus/files/private-chef-cookbooks/private-chef/providers/pg_upgrade.rb b/omnibus/files/private-chef-cookbooks/private-chef/providers/pg_upgrade.rb
index 6b364a3af6..c1647cf05e 100644
--- a/omnibus/files/private-chef-cookbooks/private-chef/providers/pg_upgrade.rb
+++ b/omnibus/files/private-chef-cookbooks/private-chef/providers/pg_upgrade.rb
@@ -54,6 +54,7 @@ def whyrun_supported?
 action :upgrade do
   if upgrade_required?
     converge_by("Upgrading database cluster") do
+      check_required_disk_space unless ENV['CS_SKIP_PG_DISK_CHECK'] == "1"
       shutdown_postgres
       initialize_new_cluster
       update_to_latest_version
@@ -123,6 +124,37 @@ def upgrade_required?
   end
 end
 
+#
+# Since we don't use the --link flag, we need to ensure the disk has
+# enough space for another copy of the postgresql data.
+#
+def check_required_disk_space
+  old_data_dir_size = Du.du(old_data_dir)
+  # new_data_dir might not exist at the point of making this check.
+  # In that case check the first existing directory above it.
+  new_dir = dir_or_existing_parent(new_data_dir)
+  free_disk_space = Statfs.new(new_dir).free_space
+
+  if old_data_dir_size < (free_disk_space * 0.90)
+    Chef::Log.debug("Old data dir size: #{old_data_dir_size}")
+    Chef::Log.debug("  Free disk space: #{free_disk_space}")
+    Chef::Log.debug("Free space is sufficient to start upgrade")
+    true
+  else
+    Chef::Log.fatal("Insufficient free space on disk to complete upgrade.")
+    Chef::Log.fatal("The current postgresql data directory contains #{old_data_dir_size} KB of data but only #{free_disk_space} KB is available on disk.")
+    Chef::Log.fatal("The upgrade process requires at least #{old_data_dir_size/0.90} KB.")
+    raise "Insufficient Disk Space to Upgrade"
+  end
+end
+
+def dir_or_existing_parent(dir)
+  return dir if ::File.exist?(dir)
+  return dir if ::File.expand_path(dir) == "/"
+
+  dir_or_existing_parent(::File.expand_path("#{dir}/.."))
+end
+
 # If a pre-existing postgres service exists it will need to be shut
 # down prior to running the upgrade step.
 def shutdown_postgres