Q

How to create a snapshot from NAS and SAN of Oracle database

An SAP administrator wants to create a snapshot of an Oracle database that is consistent from both a SAN and NAS.

I have SAP with Oracle running on Solaris with a Java front end. My data resides on both NAS (NFS) and a SAN on the same storage array.

I need to create a local consistent snapshot from both the NAS and SAN at the same time. Currently, I can do a

consistent snapshot from the array, but it may not reflect any in-flight data that isn't flushed from the host or NAS head.

Is there a way to ensure a consistent snapshot with a script that would pause or quiesce the host?

The most important technical component in a SAP environment is always the database. If all fails, and you succeed in restoring your database, all other SAP components can be reconstructed in a worst-case scenario with a re-install of the SAP instances.

In your setup, put the Oracle database in suspend mode. When done, all I/O is suspended.

As long as the database is in suspend mode, SAP is in reconnect mode. As such, both SAP and database are 'waiting' and nothing is written to the database and SAP application file systems.

At that point, split the mirrors in both NAS and SAN and start your backup on the mirrors. If you resume the database, all activities continue as if nothing happened in between.

In addition, if you disable file system buffering at the OS level, all I/Os are written to the disks at database commit time. File system buffering is no longer used. This guarantees consistent backups.

Consult your OS documentation on the disabling of file system buffering. For the suspend/resume feature, consult the Oracle documentation.

For more information on backup/recovery from SAP, see http://service.sap.com/atg --> backup/restore.

This was first published in January 2009

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