23 DRBD #

1. Make sure the block devices in your Linux nodes are ready and partitioned (if needed).

2. If your disk already contains a file system that you do not need anymore, destroy the file system structure with the following command:

   # dd if=/dev/zero of=YOUR_DEVICE count=16 bs=1M

   If you have more file systems to destroy, repeat this step on all devices you want to include into your DRBD setup.

3. If the cluster is already using DRBD, put your cluster in maintenance mode:

   # crm maintenance on

   If you skip this step when your cluster already uses DRBD, a syntax error in the live configuration leads to a service shutdown. Alternatively, you can also use drbdadm -c FILE to test a configuration file.

Beginning with DRBD version 8.3, the former configuration file is split into separate files, located under the directory /etc/drbd.d/.

1. Open the file /etc/drbd.d/global_common.conf. It contains already some global, pre-defined values. Go to the startup section and insert these lines:

   startup {
       # wfc-timeout degr-wfc-timeout outdated-wfc-timeout
       # wait-after-sb;
       wfc-timeout 100;
       degr-wfc-timeout 120;
   }

   These options are used to reduce the timeouts when booting, see https://docs.linbit.com/docs/users-guide-9.0/#ch-configure for more details.

2. Create the file /etc/drbd.d/r0.res. Change the lines according to your situation and save it:

   resource r0 { 1
     device /dev/drbd0; 2
     disk /dev/disk/by-id/example-disk1; 3
     meta-disk internal; 4
     on alice { 5
       address  192.168.1.10:7788; 6
       node-id 0; 7
     }
     on bob { 5
       address 192.168.1.11:7788; 6
       node-id 1; 7
     }
     disk {
       resync-rate 10M; 8
     }
     connection-mesh { 9
       hosts alice bob;
     }
     net {
       protocol C; 10
       fencing resource-and-stonith; 11
      }
     handlers { 12
       fence-peer "/usr/lib/drbd/crm-fence-peer.9.sh";
       after-resync-target "/usr/lib/drbd/crm-unfence-peer.9.sh";
      }
   }

   1	DRBD resource name that allows some association to the service that needs them. For example, nfs, http, mysql_0, postgres_wal, etc. Here a more general name r0 is used.
   2	The device name for DRBD and its minor number. In the example above, the minor number 0 is used for DRBD. The udev integration scripts will give you a symbolic link /dev/drbd/by-res/nfs/0. Alternatively, omit the device node name in the configuration and use the following line instead: drbd0 minor 0 (/dev/ is optional) or /dev/drbd0
   3	The raw device that is replicated between nodes. Note, in this example the devices are the same on both nodes. If you need different devices, move the disk parameter into the on host.
   4	The meta-disk parameter usually contains the value internal, but it is possible to specify an explicit device to hold the meta data. See https://docs.linbit.com/docs/users-guide-9.0/#s-metadata for more information.
   5	The on section states which host this configuration statement applies to.
   6	The IP address and port number of the respective node. Each resource needs an individual port, usually starting with 7788. Both ports must be the same for a DRBD resource.
   7	The node ID is required when configuring more than two nodes. It is a unique, non-negative integer to distinguish the different nodes.
   8	The synchronization rate. Set it to one third of the lower of the disk- and network bandwidth. It only limits the resynchronization, not the replication.
   9	Defines all nodes of a mesh. The hosts parameter contains all host names that share the same DRBD setup.
   10	The protocol to use for this connection. Protocol C is the default option. It provides better data availability and does not consider a write to be complete until it has reached all local and remote disks.
   11	Specifies the fencing policy resource-and-stonith at the DRBD level. This policy immediately suspends active I/O operations until STONITH completes.
   12	Enables resource-level fencing to prevent Pacemaker from starting a service with outdated data. If the DRBD replication link becomes disconnected, the crm-fence-peer.9.sh script stops the DRBD resource from being promoted to another node until the replication link becomes connected again and DRBD completes its synchronization process.

3. Check the syntax of your configuration file(s). If the following command returns an error, verify your files:

   # drbdadm dump all

4. Copy the DRBD configuration files to all nodes:

   # csync2 -xv

   By default, the DRBD configuration file /etc/drbd.conf and the directory /etc/drbd.d/ are already included in the list of files that Csync2 synchronizes.

1. Start YaST and select the configuration module High Availability › DRBD. If you already have a DRBD configuration, YaST warns you. YaST will change your configuration and will save your old DRBD configuration files as *.YaSTsave.

2. Leave the booting flag in Start-up Configuration › Booting as it is (by default it is off); do not change that as Pacemaker manages this service.

3. If you have a firewall running, enable Open Port in Firewall.

4. Go to the Resource Configuration entry. Select Add to create a new resource (see Figure 23.2, “Resource configuration”).

   

   Figure 23.2: Resource configuration #

    

   The following parameters need to be set:

   Resource Name

   The name of the DRBD resource (mandatory)

   Name

   The host name of the relevant node

   Address:Port

   The IP address and port number (default 7788) for the respective node

   Device

   The block device path that is used to access the replicated data. If the device contains a minor number, the associated block device is usually named /dev/drbdX, where X is the device minor number. If the device does not contain a minor number, make sure to add minor 0 after the device name.

   Disk

   The raw device that is replicated between both nodes. If you use LVM, insert your LVM device name.

   Meta-disk

   The Meta-disk is either set to the value internal or specifies an explicit device extended by an index to hold the meta data needed by DRBD.

   A real device may also be used for multiple DRBD resources. For example, if your Meta-Disk is /dev/disk/by-id/example-disk6[0] for the first resource, you may use /dev/disk/by-id/example-disk6[1] for the second resource. However, there must be at least 128 MB space for each resource available on this disk. The fixed metadata size limits the maximum data size that you can replicate.

   All of these options are explained in the examples in the /usr/share/doc/packages/drbd/drbd.conf file and in the man page of drbd.conf(5).

5. Click Save.

6. Click Add to enter the second DRBD resource and finish with Save.

7. Close the resource configuration with Ok and Finish.

8. If you use LVM with DRBD, it is necessary to change some options in the LVM configuration file (see the LVM Configuration entry). This change can be done by the YaST DRBD module automatically.

   The disk name of localhost for the DRBD resource and the default filter will be rejected in the LVM filter. Only /dev/drbd can be scanned for an LVM device.

   For example, if /dev/disk/by-id/example-disk1 is used as a DRBD disk, the device name will be inserted as the first entry in the LVM filter. To change the filter manually, click the Modify LVM Device Filter Automatically check box.

9. Save your changes with Finish.

10. Copy the DRBD configuration files to all nodes:

    # csync2 -xv

    By default, the DRBD configuration file /etc/drbd.conf and the directory /etc/drbd.d/ are already included in the list of files that Csync2 synchronizes.

1. On both nodes (alice and bob), initialize the meta data storage:

   # drbdadm create-md r0
   # drbdadm up r0

2. To shorten the initial resynchronization of your DRBD resource check the following:

   • If the DRBD devices on all nodes have the same data (for example, by destroying the file system structure with the dd command as shown in Section 23.3, “Setting up the DRBD service”), then skip the initial resynchronization with the following command (on both nodes):

     # drbdadm new-current-uuid --clear-bitmap r0/0

     The state will be Secondary/Secondary UpToDate/UpToDate

   • Otherwise, proceed with the next step.

3. On the primary node alice, start the resynchronization process:

   # drbdadm primary --force r0

4. Check the status with:

   # drbdadm status r0
   r0 role:Primary
     disk:UpToDate
     bob role:Secondary
     peer-disk:UpToDate

5. Create your file system on top of your DRBD device, for example:

   # mkfs.ext3 /dev/drbd0

6. Mount the file system and use it:

   # mount /dev/drbd0 /mnt/

1. Start the crm interactive shell:

   # crm configure

2. Create a primitive for the DRBD resource r0:

   crm(live)configure# primitive drbd-r0 ocf:linbit:drbd \
     params drbd_resource="r0" \
     op monitor interval=15 role=Promoted \
     op monitor interval=30 role=Unpromoted

3. Create a promotable clone for the drbd-r0 primitive:

   crm(live)configure# clone cl-drbd-r0 drbd-r0 \
     meta promotable="true" promoted-max="1" promoted-node-max="1" \
     clone-max="2" clone-node-max="1" notify="true" interleave=true

4. Commit this configuration:

   crm(live)configure# commit

5. Exit the interactive shell:

   crm(live)configure# quit

1. Open a terminal console, then log in as root.

2. Test the configuration file by running drbdadm with the -d option. Enter the following command:

   # drbdadm -d adjust r0

   In a dry run of the adjust option, drbdadm compares the actual configuration of the DRBD resource with your DRBD configuration file, but it does not execute the calls. Review the output to make sure you know the source and cause of any errors.

3. If there are errors in the /etc/drbd.d/* and drbd.conf files, correct them before continuing.

4. If the partitions and settings are correct, run drbdadm again without the -d option.

   # drbdadm adjust r0

   This applies the configuration file to the DRBD resource.