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SAP MaxDB Backup/ Recovery Interview Questions and Answer

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SAP MaxDB Backup/ Recovery Interview Questions and Answer
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Which are the types of database backups?

An incremental data backup backs up all the data in the data area that has been changed since the last complete data backup.

Is the log area also saved during the data backup?

No. A data backup using the MaxDB tool only backups the data that is stored in the data area. This includes the actual application data and the images.

What should I remember in the back of my mind when I use tapes to backup data?

We should ensure that we do not use NOREWIND tapes to backup data.

What are options do I have for saving the log area?

We have two options:

A: Automatic Log Backup- As soon as a log segment is full in the log area the database system saves this log segment to a version file. Monitoring is not required by the database administrator and the admin only needs to guarantee that there is always enough space for the log backups so that the backup activity is not cancelled.

B: Interactive Log Backup- MAxDB tools must be used to explicitly trigger this.

Can log area be saved into a tape?

No this feature is not supported.

Can log area be saved into a pipe?

Interactive log area can be saved into pipes.

How should I archive the log backup files?

We can use DBMCLI command archive_stage to save log backup files into an external medium.

Which MaxDB tools are available for data backup and what are the advantages?

Tools available are DBMGUOI, Database studio, or DBMCLI. We can backup datavase in online status using MaxDB tool for a system copy.

How do I check a database backup?

We can use MaxDB backup tools DBMGUI, Database studio or DBMCLI.

Does MaxDB support use of external backup tools?

Yes it supports a number of backup tools from third parties.

Does MaxDB support backup to NFS-mounted file system?

Yes and we must ensure the correct configuration for this of the NFS.

Which are the MaxDB tools for recovery?

DBMGUI, Database Studio or DBMCLI.

How is a file system backup integrated as of MaxDB Version 7.8?

As of MaxDB Version 7.8, you can include file system backups in the MaxDB backup history, which means that file system backups are also possible when the database is in online status. The database core creates a a MaxDB snapshot to establish the I/O consistency using a data backup to a backup template with the device type EXTERNAL.
You can then perform the file system backup, and you must explicitly inform the database of its success or failure using the DBM server command backup_finish.

In this way, you can perform the initial data backup as a file system backup also.

Where can I find a how-to for the backup process with DBMCLI?

A how-to for the backup process with DBMCLI is provided on the SAP Community Network (SCN) at:

wiki.sdn.sap.com/wiki/x/sx0B

How do I check a database backup?

You can use the MaxDB backup tools DBMGUI, Database Studio, or DBMCLI to check whether a backup can be imported and therefore, whether it can be used for a recovery.
In this case, the service database is used to import the entire backup. The operation of the database must not be interrupted during this process.

You will find more information about this in the glossary of the MaxDB documentation ( 767598) under the key word "Backup", in the Database Studio manual under the title "Checking Backups", as well as in the DBMCLI manual under the DBM command recover_check.

Does MaxDB support the use of external backup tools?

Yes. Max DB supports a number of backup tools from third parties, such as Networker, Netbackup from Veritas, and so on.

Which specific tools are supported, and how they can be included in a MaxDB environment is described in the MaxDB documentation (767598)? Search the glossary for the keyword "external backup tool".

Scripts in the database manager also enable you to use all other backup tools that are able to process backups from pipes.

If you save the log area with external backup tools (interactive log backup), see 1392043.

Is a compressed database backup an option?

As of MaxDB Version 7.8, you can also create compressed database backups. To do this, choose the option COMPRESSED when defining the backup template. During the compression, the the databases use the gzip default compression level. Whether the compression increases or optimizes the backup time greatly depends on the data to be backed up.

Does MaxDB support backups to NFS-mounted file systems?

Yes. For this, you must ensure the correct configuration of the Network File System (NFS) server. For more information, see 912905 FAQ: Storage systems used with MaxDB.

What is a database snapshot?

A database snapshot freezes the current status of the database area. After you have made a snapshot, you can continue to use the data of the database instance as normal and change data without this affecting the snapshot. At a later time, you can return to the status of the data area at the time of the snapshot. The snapshot contains all of the required information. You do not require a complete data backup for this.

A snapshot is NOT a data backup. To be able to recover your data following damage to the data area, you must regularly back up your data and logs.

Which MaxDB tools are available for a recovery?

The MaxDB tools DBMGUI, Database Studio, or DBMCLI are available for a recovery (RESTORE DATA, RESTORE LOG).

For interactive recovery processes, you can use the Recovery Wizard in DBMGUI or Database Studio. The Recovery Wizard proposes the optimal recovery strategy.

You have the option to restore the database only up to a certain consistent status (RESTORE UNTIL). You can use an option to specify up to what point in time the entries should be imported from the log backups or, if necessary, from the log area.

Where can I find a how-to for the recovery process with DBMCLI?

A how-to for the recovery process with DBMCLI is provided on the SAP Community Network (SCN) at:

wiki.sdn.sap.com/wiki/x/jh4B

Can I execute a RESTORE LOG without having imported a suitable data backup?

No, log backups require a setup point in the data area in order to track or roll back transactions. If this setup point cannot be found, you cannot track the log area.

What have I done wrong if the system issues error message 8003 'LOG and Data must be compatible'?

Log-entries (After Images) and data of an instance must always be compatible. The data of an instance may not be mixed with log entries (After Images) from another instance in the case of a Restore Log.

To avoid incompatibility between log entries and data, the database kernel writes the DBIdent to

- The restart record in the second block of the first data volume,
- The log info page in the second block of the first log volume,
- Every data backup (Save Data/Save Pages)
- Every log backup.

DBIdent contains the name of the database server, the name of the database instance, and a time stamp for when the backup history started. This time stamp is, for example, set the first time a database instance is restarted, and at the end of a Restore Log with Until specifications.

The name of the database server and the instance name do not need to correspond to the current server or the current instance name. You can rename database instances without changing the DBIdent (see 604680).

Restart after recovery only works if the DBIdent in the log area matches the DBIdent in the data area or if the log area has been initialized.

If the log entries and data do not match, the database cannot be started and the restart terminates with error message 8003 'Log and Data must be compatible'.

What does the recovery process look like when a log volume is lost (for example, due to disk errors)?

Without a copy of the log area (using database tools or based on the hardware), data is lost when a log volume is lost because the log area that has not yet been saved cannot be used for a recovery. To keep the loss of data as small as possible, execute a data backup in the state ADMIN. This saves all changes that were stored in the data area with the last savepoint. To recover the database, choose the recovery with initialization and use this backup. The loss of data includes the period as of the last savepoint, which you can determine using the detailed information for this backup under 'Last Save Point' (Database Studio -> Administration -> Backup -> Details or DBMCLI command backup_history_list).

If a data backup in the state ADMIN is no longer possible because the data volumes are also affected by the disk error, you must execute a recovery with initialization using the last data backup and all of the following log backups. In this case, the loss of data includes the period as of the last log backup.

Where can I find more information about MaxDB backup/recovery?

You can find more information about MaxDB backup/recovery in glossary of the MaxDB documentation ( 767598) under the keywords 'Backup' and 'Recover'.

Alternatively, you can use the SDN to access the MaxDB documentation at:

sdn.sap.com/irj/sdn/maxdb


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