LOTC Disk Replication Consistency

1	Alarm Description
2	Procedure
2.1	Handle Alarm LOTC Disk Replication Consistency

1 Alarm Description

The alarm is raised when the control node pair has operated with inconsistent data for more than 20 minutes. The control node pair is in a non-redundant mode when its data is inconsistent.

Table 1 LOTC Disk Replication Consistency Alarm Causes
Alarm Cause	Description	Fault Reason	Fault Location	Impact
Inconsistent data in control node pair for more than 20 minutes	The control nodes have operated with inconsistent data for more than 20 minutes despite having connection with each other	Network failure leading to communication problems between the control nodes	Network	Both controllers take the primary role and no data is transferred between the nodes
		Disk mirroring failure leading to disk inconsistency between the control nodes	Disk failure	No immediate impact. If the node with the current data goes down, the cluster does not have a controller node containing redundant data which it can fail over to.
		Hardware failure on the secondary control node	Secondary control node	If one of the controller nodes is down, the cluster does not have a controller node with consistent data which it can fail over to

Note:: This alarm can appear as a result of a maintenance activity.

2 Procedure

2.1 Handle Alarm LOTC Disk Replication Consistency

Prerequisites

This instruction references the following documents:
- Data Collection Guideline
- LOTC Disk Replication Communication
No tools are required.
The following condition must apply:
- The alarm is raised.

Steps

Is the alarm raised during initial installation or replacement of a control node?
Yes: Proceed with Step 3.

No: Continue with the next step.
Is the Disk Replication Communication alarm raised?
Yes: The consistency fault is most likely caused by a communication problem. Further actions are outside the scope of this instruction. Follow the procedure in LOTC Disk Replication Communication to clear the LOTC Disk Replication Communication alarm.

No: Continue with the next step.
Log on to the host to access a Linux® shell:
ssh <user>@<hostname>

The hostname is part of alarm attribute Source.
Check that disk synchronization is ongoing:
drbdadm status

The following is an example output:
drbd0 role:Primary disk:UpToDate SC-2 role:Secondary replication:SyncSource peer-disk:Inconsistent done:65.20
Note:
Synchronization is ongoing if the value after done: is increasing.
On each control node, command drbdadm status provides detailed information about the disk synchronization progress.

A complete disk synchronization is performed, which can take up to five hours to complete. The time to complete a disk synchronization depends on the following:
- How much data that has not been synchronized
- Disk size, disk speed, and network speed
During disk synchronization, the control nodes are not redundant.
Is the value after done: increasing and eventually reaching 100%?
Yes: Continue with the next step.

No: Proceed with Step 7.
Is the alarm cleared?
Yes: Proceed with Step 12.

No: Proceed with Step 10.
Identify the Distributed Replicated Block Device (DRBD) interfaces as follows:
1. Get the name of the interface (eth<x>):
  cat /etc/cluster/nodes/this/networks/internal/primary/interface/name
  
  The following is an example output:
  eth0
2. Get the IP address (<ip>):
  cat /etc/cluster/nodes/this/networks/internal/primary/address
  
  The following is an example output:
  169.254.43.11
3. Get the network mask (<netmask>):
  cat /etc/cluster/nodes/this/networks/internal/primary/network/netmask
  
  The following is an example output:
  255.255.255.0

Check the log /var/log/messages for recent system log messages indicating DRBD interface-related issues, for example (to show the last 1000 lines in the log):

tail -1000 /var/log/messages

The following is an example output in a faulty situation with network interface issues:

Aug 26 12:17:52 SC-1 kernel: [  277.720545] hrtimer: interrupt took 572013 ns
Aug 26 12:32:50 SC-1 kernel: [ 1175.612842] tipc: Resetting bearer <eth:eth0>
Aug 26 12:32:50 SC-1 dhcpd: receive_packet failed on eth0: Network is down
Aug 26 12:32:50 SC-1 syslog-ng[1810]: I/O error occurred while writing; fd='6', error='Network ⇒
is unreachable (101)'
Aug 26 12:32:50 SC-1 syslog-ng[1810]: Connection broken; time_reopen='10'
Aug 26 12:32:59 SC-1 ntpd[2240]: sendto(192.0.2.10) (fd=23): Network is unreachable
Aug 26 12:33:00 SC-1 syslog-ng[1810]: Connection failed; error='Network is unreachable (101)'
Aug 26 12:33:00 SC-1 syslog-ng[1810]: Initiating connection failed, reconnecting; time_reopen='10'
Aug 26 12:33:10 SC-1 syslog-ng[1810]: Connection failed; error='Network is unreachable (101)'
Aug 26 12:33:10 SC-1 syslog-ng[1810]: Initiating connection failed, reconnecting; time_reopen='10'
Aug 26 12:33:20 SC-1 syslog-ng[1810]: Connection failed; error='Network is unreachable (101)'
Aug 26 12:33:20 SC-1 syslog-ng[1810]: Initiating connection failed, reconnecting; time_reopen='10'

Note:: In this output, eth0 is the interface used by the DRBD.

Are there any issues with the network interface used for the DRBD?
Yes: The consistency fault is most likely caused by a communication problem. Further actions are outside the scope of this instruction. Follow the procedure in LOTC Disk Replication Communication to clear the LOTC Disk Replication Communication alarm, which is to be raised within 20 minutes if not raised yet.

No: Continue with the next step.
Perform data collection, refer to Data Collection Guideline.
Consult the next level of maintenance support. Further actions are outside the scope of this instruction.
Job is completed.