drbd storage driver
*******************

Introduction
============

Drbd is a Linux kernel driver presenting shared block devices from pairs of local block devices. Replication data goes over the network and can be synchronous ou near-synchronous. It supports the active-active or active-passive operation modes. The former being a prerequisite for cluster filesystem.

OpenSVC does not configure the drbd framework. It just handles the actions needed upon service 'start' and 'stop'.

Node configuration
==================

The drbd resource configuration is expected to reside in :file:`/etc/drbd.d/${res}.res`.

If a vg is layered above drbd, a specific LVM configuration is recommended (link)

::

        Set write_cache_state = 0 in /etc/lvm/lvm.conf
        Remove /etc/lvm/cache/.cache

Files contributed to sync#i0
============================

::

        /etc/drbd.d/${res}.res

This file is thus replicated from the node running the service to the other nodes and drpnodes.

Command set
===========

The drbd driver is a member of the 'disk group' class.

:command:`start`

    Promote to 'primary' state

:command:`stop`

    Demote to 'secondary' state

Tags
====

:command:`prevg`

    Upon service 'start', drbd 'start' is scheduled before volume group 'start'. To use when the volume group is layered over the drbd.

:command:`postvg`

    Upon service 'start', drbd 'start' is scheduled after volume group 'start'. To use when the the drbd is layered over the volume group.

Syntax
======

::

        ##############################################################################
        #
        # 'drbd' resource
        #   Linux only. Set up the attachment, connection and role of a defined drbd
        #   resource. Depending on weather this resource is stacked over or under
        #   other disk group resources we need to start it respectively late or early.
        #   This is controlled by a set of tags: 'prevg', 'postvg'.
        #
        [drbd#0]
        
        #
        # 'res'
        #   mandatory. String. The name of the drbd resource associated with this
        #   service resource. OpenSVC expect the resource configuration file to
        #   reside in '/etc/drbd.d/resname.res'. The 'sync#i0' resource will take
        #   care of replicating this file to remote nodes.
        #
        res = data
        
        #
        # 'always_on'
        #   state the expected status on nodes specified as value is 'up'. With drbd
        #   the 'up' status is granted when the drbd driver reports UpToDate/UpToDate,
        #   so always_on should point to all nodes participating in the drbd resource.
        #
        always_on = drpnodes nodes
        
        #
        # 'tags'
        #    prevg:  upon service 'start', drbd 'start' is scheduled before volume
        #            group 'start'. To use when the volume group is layered over the
        #            drbd.
        #    postvg: upon service 'start', drbd 'start' is scheduled after volume
        #            group 'start'. To use when the the drbd is layered over the
        #            volume group.
        #
        tags = prevg

Examples
========

In this example the service drives an OpenVZ container installed in a filesystem (fs#1) build on a drbd (drbd#1, resource name 'data'). OpenSVC Also handles the :file:`svc/etc/init.d/foo` start-up script inside the vz container.

Start
-----

::

        root@deb1:/# svcmgr -s drbdsvc.opensvc.com start
        DRBD#0  INFO    drbd resource data is already up
        DRBD#0  INFO    drbdadm primary data
        FS#1    INFO    e2fsck -p /dev/drbd0
        FS#1    INFO    output:
        /dev/drbd0: clean, 27663/131072 files, 161431/524263 blocks
        
        FS#1    INFO    mount -t ext3 -o defaults /dev/drbd0 /drbdsvc
        VZ      INFO    vzctl start 101
        VZ      INFO    output:
        Starting container ...
        Container is mounted
        Adding IP address(es): 192.168.0.204
        Setting CPU units: 1000
        Set hostname: drbdsvc.opensvc.com
        Container start in progress...
        
        VZ      INFO    wait for container up status
        VZ      INFO    wait for container operational
        APP     INFO    spawn: vzctl exec 101 /svc/etc/init.d/S10foo start
        APP     INFO    start done in 0:00:00.068714 - ret 0 - logs in /var/tmp/opensvc/svc_drbdsvc.opensvc.com_S10foo.log

Stop
----

::

        APP     INFO    spawn: vzctl exec 101 /svc/etc/init.d/K90foo stop
        APP     INFO    stop done in 0:00:00.039901 - ret 0 - logs in /var/tmp/opensvc/svc_drbdsvc.opensvc.com_K90foo.log
        VZ      INFO    vzctl stop 101
        VZ      INFO    output:
        Stopping container ...
        Container was stopped
        Container is unmounted
        
        VZ      INFO    wait for container down status
        FS#1    INFO    umount /drbdsvc
        DRBD#0  INFO    drbd resource data is already up
        DRBD#0  INFO    drbdadm secondary data