maxdb disaster recovery

[michelesalern]

I have a virtual server with linux o/s sap erp and maxdb version 7.9.10.05

I do full backup daily and log backup hourly, and these files are saved in a folder on the same server that holds the sap erp engine, sap maxdb database engine and the erp database

I have 2 sites with VMware hardware replicating every 5 minutes using RP4VM software

If I execute a disaster recovery exercise by braking the link between the 2 sites and bringing the linux server server on.

Would it be wise to say that is it safe to start the maxdb and then SAP and achieve 100% consistency?

I put the question because my learning has been that if you do VMware relication that would not ensure database consistency as a proper hot standby database where logs are applied as they become available and with that ensured that a complete committed update is posted into the database and ensure 100% consistency.

I raise the question because the VMware specialist insist that by doing the constant replication between the 2 sites, with intervals of 5 minutes, it will ensure that the database will be consistent on a disaster recovery scenario

[former_member272632]

Hello Michele,

your doubts are correct: any replication without additional actions on db level will not guarantee the consistent state of the database on the replicated side. For the time of replication you need to prevent any change of the database content.

The most simple action is to disable log writing for the time of replication and enable it again after replication is done. For the time of replication the database is in read only state. All changing operations will wait until log writing is enabled again (Logwriter Suspended - MaxDB - Community Wiki (sap.com)). The dbm commands, which providing this are: "db_execute suspend logwriter" and "db_execute resume logwriter".

The commands can be executed remotely from the server which is triggering VM snapshots.

Another possibility is to run backups with the backup medium type 'EXTERNAL'. This backup type was developed for backups based on file system snapshots. It is described in 1928060 - Data backup and recovery with file system backup - SAP ONE Support Launchpad. However because you are doing replication every 5 minutes you will get huge backup history, also creating and dropping of internal database snapshots will cause unnecessary load on the database. Let me know if you are interesting in this, I can provide more details.

Regards, Alexander

[michelesalern]

Thankyou for your comment; It is just the infrastructure specialist keep pushing that VMware replication it is more than enough so we can start our SAP server in case of loosing one site and consistency will be 100%. I do not share this at all, plus my learnings with different databases indicates that only full and log backups will help you in case of loosing one site. If you can implement "always on" like MS_SQL offers then that is another way to minimize downtime and have a consistent db (this is just an example)

Thank yuo again; any other comment would be appreciated from the rest of the community