HANA Multitier System Replication – HOW TO Configure/ Take-Over / Fail-Back Setup for DR scenario

———————————————————————————————————————————

Hello All,

This is my first SAP blog post. Happy sharing knowledge. !! please do let me know if you have any suggestions to improve…

DISCLAIMER: This blog is based on due diligence performed at the time of writing. As options and paths can change over time, readers are advised to check the latest official information before making business decisions. The author accepts no responsibility for the current validity, accuracy, completeness or quality of information provided.”

———————————————————————————————————————————

I was searching for step by step HANA multi-Tier Replication fail-over and fail -back procedure for DR scenario . I read all the blog post related to multi-tier Replication, but I could not find any blog post mentioning the steps for DR scenario where both primary and secondary will not be available at same time. so thought of writing my experience on this..

In this blog post, we are going to discuss about the following

1. Pre-Requites to setup Multitier System Replication
2. How to setup Multitier HANA System Replication
3. Takeover and Failback Procedure for Multitier System Replication

HANA Version used : HANA 1.0 SP12

Before we proceed, remember…

1. Multi Target HANA Replication ( A->B, A->C) is available only from HANA 2.0 SP03

Architecture

Prerequisite to setup Multitier System Replication

I have mentioned some important prerequisite here.

• SAP HANA software version of the secondary has to be equal to or newer than the one on the primary.In terms of configuration, both Primary and secondary must be identical. Not only with number of hosts but, host roles, failover groups, etc
• SID and Instance number must be identicalHostnames in the primary system should be different to the hostnames used in the secondary systems.
• Ensure that log_mode is set to “normal”
• The required ports must be available. The same <instance number> is used for primary and secondary systems. The <instance number>+1 must be free on both systems, because this port range is used for system replication communication.
• The operation mode must be identical for all replications, a mixture (e.g. delta_datashipping from tier 1 to tier 2 and logreplay from tier 2 to tier 3) isn’t allowed
• Both systems should run on the same endianness platform
  1. How to find endianness of the VM?
     1. Run the following command – lscpu ( SUSE & RHEL)
• Please refer below link for complete list – Link

Setup Multitier HANA System Replication

In Node 1:

Step 1: Perform one full backup

Step 2: hdbnsutil -sr_enable –name=NODE1

In Node 2:

Step 1: Stop the secondary system:

sapcontrol –nr <instance_number> -function StopSystem HDB

Step 2: Register the secondary system,choose a replication mode and the

Operation mode

hdbnsutil -sr_register –remoteHost=<node1 hostname>

–remoteInstance=<instance number>

–replicationMode=<sync|syncmem|async>

– -operationMode=<delta_datashipping|logreplay> –name=SITEB

EX:

hdbnsutil -sr_register –remoteHost=hananode01 –remoteInstance=00 —                                              replicationMode=sync –operationMode=logreplay –name=NODE2

Step 3:  Start the secondary system to start replication

sapcontrol –nr <instance_number> -function StartSystem HDB

EX:

sapcontrol -nr 00 -function StartSystem HDB

NOTE: Wait till HANA Replcation from NODE -1 to NODE -2 is completed successfully and all services become ACTIVE

Step 4: in NODE02,

Execute –>  hdbnsutil –sr_enable

Note : This is to enable the replication From NODE-2 to NODE -3

In Node 3:

Step 1: Stop the HANA DB

sapcontrol –nr <instance_number> -function StopSystem HDB

Step 2: Register the secondary system,choose a replication mode and the                                                       operation mode

hdbnsutil -sr_register –remoteHost=<node2 hostname>

–remoteInstance=<instance number>

–replicationMode=<sync|syncmem|async>

–operationMode=<delta_datashipping|logreplay> –name=SITEB

EX:

hdbnsutil -sr_register –remoteHost=hananode02 –remoteInstance=00 —                                              replicationMode=async –operationMode=logreplay –name=NODE03

Step 3:  Start the secondary system to start replication

sapcontrol –nr <instance_number> -function StartSystem HDB

EX:

sapcontrol -nr 00 -function StartSystem HDB

NOTE: Wait till HANA Replcation from NODE -2 to NODE -3 is completed successfully and all

services become ACTIVE

Monitor the Replication Progress and Status:

From Primary System : ( NODE01), please run the following python script as <sid>adm

python $DIR_INSTANCE/exe/python_support/systemReplicationStatus.py

Takeover and Fail back Procedure for Multi-tier System Replication

In this blog post, We are going to discuss only about DR scenario.. ( Fail-over and fail back procedure for HA scenario. I e. NODE 1 to NODE 2.. Please refer the procedure here -> LINK )

We Consider the following situation here…

Case of Disaster, Complete Primary region is down

(OR) HANA Primary and secondary HOST is down and not accessible

Fail-Over to DR Site:

Step 1: In NODE03 , Perform the take over

hdbnsutil –sr_takeover

Step 2: HANA will be coming UP and be accessible in NODE-3 now

Step 3: Bring Your SAP application on top of HANA

Fail-Back to Primary Region:

High Level fail-Back Steps:

1. Bring your HANA VM’s UP in Primary Region
2. Register your Ex-Primary system (NODE01) with DR HANA (Current Primary- NODE03)
3. Once Reverse Replication from Node 03 to Node 01 is done, perform Take over on NODE01
4. Bring your SAP application on Primary region

There are two scenarios could be possible here…

1. Due to disaster, you may need to Re-build HANA system from scratch & Perform fail-back
   1. For this, please follow from Step 4 below
2. Bring UP existing HANA NODE-1 and NODE-2 after Issue resolved in Primary Region
   1. In this scenario, Both NODE-01 and NODE 02 still be having existing configuration. So before we register NODE01 as secondary to Node 03 , we need to clean up the existing configuration ( Bcoz, NODE01 has ROLE – PRIMARY when it went down)

Step 1:

On NODE-1 : Start HANA database ( HDB Start)

Step1 : hdbnsutil -sr_unregister –id=3

Step2 : hdbnsutil -sr_unregister –id=2

Step3 : hdbnsutil -sr_disable –force

Step4: hdbnsutil -sr_cleanup –force

Step 2:

On Node-2 VM, Don’t Start HANA Database

Step 1: hdbnsutil -sr_cleanup –force

Replication status should be “NONE”

Step 3:

On NODE03, by Default Replication should have been enabled. In case if not please execute the following command

hdbnsutil -sr_enable –name=NODE3

Step 4:

On NODE01,

Step 1: Stop HANA ( HDB stop)

Step 2: Register the secondary system,choose a replication mode and the operation mode

hdbnsutil -sr_register –remoteHost=<node3 hostname>

–remoteInstance=<instance number>

–replicationMode=<sync|syncmem|async>

–operationMode=<delta_datashipping|logreplay> –name=SITEA

EX:

hdbnsutil -sr_register –remoteHost=hananode03 –remoteInstance=00 –replicationMode=Async – -operationMode=logreplay –name=NODE01

Step 3:  Start the secondary system to start replication

sapcontrol –nr <instance_number> -function StartSystem HDB

EX:

sapcontrol -nr 00 -function StartSystem HDB

NOTE: Wait till HANA Replication from NODE -3 to NODE -1 is completed successfully and all services become ACTIVE

Step 5: Once Fail-Back decision from DR Site to PRIMARY Site is made, please execute the following command in NODE01

Step 1: In NODE01 , Perform the take over

hdbnsutil –sr_takeover

Step 2: HANA will be coming UP and be accessible in NODE-01 now

Step 3: Bring Your SAP application on top of HANA NODE 01

So now at this point business started running on Primary region (NODE01) again &  We can now re-Establish the Multi-tier Replication again (NODE 01 ->NODE 02 -> NODE 03) to setup HA and DR

—————–

References

• 1999880 – FAQ: SAP HANA System Replication
• 2057595 – FAQ: SAP HANA High Availability
• System replication guide
• Troubleshoot System Replication
• How To Perform System Replication for SAP HANA
• Network Configuration for SAP HANA System Replication