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Questions on HANA System Replication

Hi All,

I would like to seek your input/advise, if I setup HA=DR (between 2 datacenters) using system replication from PRD (primary) to DEV/QAS (secondary) utilizing shadow operation i.e like the following diagram.

My questions are:

1. Do the HANA System Replication sync. real time?

2. May I know what is the minimum number/minute that I can set to replicate both data disk and log disk from primary host to secondary host?

3. How long do you think the transition period from primary host to secondary host? any chance for un-interrupted/instant takeover? if not, how long do you think it will be?

4. I read once the secondary host takes over the primary, the existing non-prod operation will be ended. is it done automatically or we need to do it manually?

5. How do we switch back again to the primary host (from secondary host)? I'm assuming in here we need to do it via HANA Studio.

Thank you,

Regards,

Ura

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2 Answers

  • Best Answer
    Posted on May 28, 2015 at 05:27 AM

    Dear Ura,

    Answer to your following questions differs from one customer to the other based on their business and system SLA, infrastructure, distance between primary & DR, etc......

    2. May I know what is the minimum number/minute that I can set to replicate both data disk and log disk from primary host to secondary host?

    3. How long do you think the transition period from primary host to secondary host? any chance for un-interrupted/instant takeover? if not, how long do you think it will be?

    Answer to some of your questions:-

    1. Do the HANA System Replication sync. real time?

    ISAP HANA system replication can be set to SYNC with commit option but it is not recommended if you don't want your application in production system to wait for the COMMIT in DR system.

    4. I read once the secondary host takes over the primary, the existing non-prod operation will be ended. is it done automatically or we need to do it manually?

    Always you can script (execute OS level DB commands in sequence) to perform this activity. Some hardware vendors offer automated option. But do you really want to automatically bring down your non-production systems during production DR scenario. I am sure your developers will not be happy 😕

    5. How do we switch back again to the primary host (from secondary host)? I'm assuming in here we need to do it via HANA Studio.

    Yes fail over back to primary host can be done through HANA studio.

    Please read from the following links for more information about SAP HANA backup and recovery.

    http://help.sap.com/saphelp_hanaplatform/helpdata/en/c4/663eabbb571014923a90c70cec566c/content.htm

    SAP HANA Backup/Recovery Overview | SCN

    Regards,

    Mat.

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  • author's profile photo Former Member
    Former Member
    Posted on May 28, 2015 at 07:02 PM

    Hi Ura,

    I agree with comments from Mathan and have a few more comments that could help:

    1. Do the HANA System Replication sync. real time?

    Comment: We have 3 modes of System Replication SYNC, SYNCMEM and ASYNC

    Depending on the latency between the Primary and Secondary Datacenter you may choose the appropriate settings

    SYNC mode can be used if your Datacenters are less than 100 KM apart

    ------------------------------------------------------------------------------------------------------------------------------

    2. May I know what is the minimum number/minute that I can set to replicate both data disk and log disk from primary host to secondary host?

    Comment: In either of the 3 modes of System Replication mentioned above you will not be able to change the timing of the replication. HANA is responsible for replicating the data depending on the mode chosen during the setup, the mode can be changed post the setup as well

    -------------------------------------------------------------------------------------------------------------------------------

    3. How long do you think the transition period from primary host to secondary host? any chance for un-interrupted/instant takeover? if not, how long do you think it will be?

    Comment: The transition from Primary to secondary depends on the size of Database, amount of data being replicated and to be committed at the time of interruption. During our tests we noticed the failover took anywhere between 2 mins to 10 mins using the SYNC mode of replication with some active connections doing writes on the source HANA system. so it really depends on several things but the SYNC mode will help you to synchronize upto most recent source system state

    ----------------------------------------------------------------------------------------------------------------------------

    4. I read once the secondary host takes over the primary, the existing non-prod operation will be ended. is it done automatically or we need to do it manually?

    Comment: I do not think this is automatic by design, it has to be done manually or could be done using scripts as Mathan mentioned in his response

    ------------------------------------------------------------------------------------------------------------------------------

    5. How do we switch back again to the primary host (from secondary host)? I'm assuming in here we need to do it via HANA Studio.

    Comment: The moment you do a TAKEOVER(term for failover) from source(SYSTEMA) to destination(SYSTEMB) the source system does not have any more connections left to the destination system. At this point you will need to setup SYSTEM REPLICATION in the reverse direction with SYSTEMB as source and SYSTEMA as destination and do a planned takeover on SYSTEMA to make it the source system. This is not automated

    -------------------------------------------------------------------------------------------------------------------------------

    Refer the How to setup SYSTEM REPLICATION document from SAP for detail explanation :

    http://www.sdn.sap.com/irj/scn/go/portal/prtroot/docs/library/uuid/9049e009-b717-3110-ccbd-e14c277d84a3?QuickLink=index&overridelayout=true&60155311981469

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    • Thanks for the inut, Sunil.

      I've something on my mind on the PRE-PROD appliance based on the system replication guidance,

      *assuming DEV/QA is my PRE-PROD.

      it says independent disk volume is needed for DEV/QAS, by any chance do you know how big the recomendation of the disk space? assuming my PRD instance having 1TB disk storage, should the pre-prod instance is 2TB or 1.5TB of disk space?

      Thank you,

      Regards,

      Ura