LOTC Disk Replication Consistency

1	Introduction
1.1	Alarm Description
1.2	Prerequisites
2	Procedure

1 Introduction

This instruction concerns alarm handling.

1.1 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.

The possible alarm causes and fault locations are explained in Table 1.

Table 1 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.

The alarm attributes are listed and explained in Table 2.

Table 2 Alarm Attributes
Attribute Name	Attribute Value
Major Type	193
Minor Type	3341942790
Source	`ManagedElement=<node_name>,HostName=<hostname>,ERIC-LINUX_CONTROL-*`
Specific Problem	LOTC Disk Replication Consistency
Event Type	environmentalAlarm (6)
Probable Cause	x736UnspecifiedReason (418)
Additional Text	One of the following: Disk not consistent for `<value>` minutes Status unknown
Perceived Severity	minor (5)

1.2 Prerequisites

This section provides information on the documents, tools, and conditions that apply to the procedure.

1.2.1 Documents

This instruction references the following documents:

1.2.2 Tools

No tools are required.

1.2.3 Conditions

Before starting this procedure, ensure that the following condition is met:

A LOTC Disk Replication Consistency alarm is raised.

2 Procedure

Do the following:

Is the alarm raised during initial installation or replacement of a control node?
Yes: Proceed with Step 4.

No: Continue with the next step.
Check the active alarm list.
For information how to check the active alarm list, refer to Check Alarm Status.
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> -p 22

The hostname is part of alarm attribute Source.

Check that disk synchronization is ongoing:

cat /proc/drbd

The following is an example output:

version: 8.4.2 (api:1/proto:86-101)
GIT-hash: 7ad5f850d711223713d6dcadc3dd48860321070c build by root@lixia, 2012-09-19 16:40:30
 0: cs:SyncSource ro:Primary/Secondary ds:UpToDate/Inconsistent C r---n-
    ns:371204 nr:0 dw:252 dr:373273 al:11 bm:31 lo:0 pe:6 ua:1 ap:0 ep:1 wo:f oos:68164
    [================>...] sync'ed: 85.2% (68164/438684)K
    finish: 0:00:05 speed: 11,692 (11,576) K/sec

Note:

Synchronization is ongoing if the value after sync'ed: is increasing.

On each control node, file /proc/drbd 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 sync'ed:, increasing and eventually reaching 100%?
Yes: Continue with the next step.

No: Proceed with Step 8.
Is the alarm cleared?
Yes: Proceed with Step 13.

No: Proceed with Step 11.
Identify the Distributed Replicated Block Device (DRDB) 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 DRDB.

Are there any issues with the network interface used for the DRDB?
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.