upgrading 1.8.0r-55 ubuntu cluster to 1.8.1-798-rel wipes out the config and data files

farshid@ubu-0105:~$ sudo dpkg -i couchbase-server-community_x86_64_1.8.1-798-rel.deb
(Reading database ... 138430 files and directories currently installed.)
Preparing to replace couchbase-server 1.8.0r (using couchbase-server-community_x86_64_1.8.1-798-rel.deb) ...

• Stopped couchbase-server
  Upgrading previous couchbase ... (1.8.0r)
  Stopping previous couchbase ... (1.8.0r)
• Stopped couchbase-server
  Saving previous couchbase config.dat ...
  Cleaning symlinks ...
  Unpacking replacement couchbase-server ...
  Setting up couchbase-server (1.8.1) ...
  Upgrading couchbase-server ...
  /opt/couchbase/bin/cbupgrade -c /opt/couchbase/var/lib/couchbase/config -a yes
  Automatic mode: running without interactive questions or confirmations.
  Upgrading your Couchbase Server to 1.8.1-798-rel.
  The upgrade process might take awhile.
  Analysing...
  Previous config.dat file is /opt/couchbase/var/lib/couchbase/config/config.dat.debsave
  Target node: ns_1@127.0.0.1
  Done: previous node configuration is empty.
• Started couchbase-server

You have successfully installed Couchbase Server.
Please browse to http://ubu-0105:8091/ to configure your server.
Please refer to http://couchbase.com for additional resources.

Please note that you have to update your firewall configuration to
allow connections to the following ports: 11211, 11210, 11209, 4369,
8091 and from 21100 to 21299.

By using this software you agree to the End User License Agreement.
See /opt/couchbase/LICENSE.txt.

Processing triggers for ureadahead ...