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 drbd driver has provisioning capabilities.

OpenSVC also includes a drbd pool driver, to automatically provision drbd-replicated volumes from a volume group, a zpool or a directory.

Node configuration

The drbd resource configuration is expected to reside in /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.

start

Promote to ‘primary’ state

stop

Demote to ‘secondary’ state

shutdown

Demote to ‘unconfigured’ state

Example

[disk#1]
type = lv
name = lv1
vg = vg1
size = 190m
standby = true

[disk#2]
type = drbd
res = res1
disk = /dev/vg1/lv1
standby = true

  • The drbd and underlying logical volume resources must be configured for standby=true. This make sure the lv is available for drbd on the slave nodes and the drbd is in secondary state.

  • The logical volume resource id (disk#1) is sorted before the drbd resource id (disk#2), so the logical volume starts before the drbd.