This is my first blog:)
I have been trying to achieve reverse replication in HANA 3 tier replication environment avoiding full sync. I have referred many HANA replication blogs and thought to write one having clear picture how it works.
Here we have 3 Sites
Site A to Site B (Replication type : SyncMem, operation mode : logreplay)
SiteB to Site C (Replication type : Async, operation mode : logreplay)
Below is the graphical representation for DR drill which is performed
Before starting DR drill we need to set below parameter on all 3 Site and restart DB
enable_log_retention = force_on_takeover
So that log will be retained during replication for all direct secondaries until a takeover is executed.
for more information on above parameter you can refer below link
Starting DR drill
- Take backup of Site A (Primary DB)
- Verify the evidence which needs to be validate on DR
- Stop sap application
- Verify that all sites are in sync
5. Stop DB of siteA
6. login to Site B and perform takeover
after takeover is performed. you can check replication between SiteB and SiteC must be still active (This can be verify from SiteB)
7. Now shutdown DB of SiteB using HDB Stop
8. Login to SiteC and perform takeover
Once takeover is performed, we have to do reverse replication now
9. Login to Site B and click register secondary system
Here do not release initiate full data shipping to avoid full sync.
This will start the delta replication between SiteC to SiteB
10. Now, Enable replication on SiteB so that we can register SiteA to SiteB as tertiary.
Login to Site B and click enable replication
11. Now login to SiteA and click register secondary system
This will start full sync between SiteB to SiteA but as both are in same datacenter it will complete in short time
This will setup the reverse replication from Site C to Site B to Site A
Now we can do fall back once all the testing is completed on Site C
Below are the steps
- Shutdown Site C
- Perform Takeover on Site B
- shutdown Site B
- Perform Takeover on Site A
- Register Site B to Site A (This will be delta sync)
- Enable replication on Site B
- Register Site C to Site B (This will be full sync)
- Once DR drill is completed you can revert the parameter enable_log_retention same as before.
With above mentioned steps we have save larger amout of time taken in Full sync during HANA DB replication.
Also can complete the DR testing in shorter time duration.
More over transaction performed in DR is not loss due to reverse replication. ?
Hope this is helpful.