How VERITAS Database FlashSnap Works

You can use VERITAS Database FlashSnap to implement point-in-time copy solutions for enterprise databases. Database FlashSnap offers you a flexible way to efficiently manage multiple point-in-time copies of your data, and reduce resource contention on your business-critical servers.

Database FlashSnap allows database administrators to create a consistent copy of a database without root privileges by creating a snapshot. A snapshot copy of the database is referred to as a database snapshot.

You can use a database snapshot on the same host as the production database or on a secondary host sharing the same storage. A database snapshot can be used for off-host processing applications, such as backup, data warehousing, and decision-support queries. When the snapshot is no longer needed, the database administrator can import the original snapshot back to the primary host and resynchronize the snapshot to the original database volumes. Database FlashSnap also allows you to resynchronize your original database volumes from the data in the snapshot if the original volumes become corrupted. This is referred to as reverse resynchronization.

Database FlashSnap can significantly reduce the time it takes to backup your database, increase the availability of your production database, and still maintain your production database's performance.

To use Database FlashSnap, you must first configure the volumes used by the database. See Preparing Hosts and Storage for Database FlashSnap, for more information.

Typical Problems Database FlashSnap Solves

Database FlashSnap is designed to enable you to use database snapshots to overcome the following types of problems encountered in enterprise database environments:

• In many companies, there is a clear separation between the roles of system administrators and database administrators. Creating database snapshots typically requires superuser (root) privileges, privileges that database administrators do not usually have.
• In some companies, database administrators are granted root privileges, but managing storage is typically not central to their job function or their core competency.
• Creating database snapshots is a complex process, especially in large configurations where thousands of volumes are used for the database. One mistake can render the snapshots useless.

Because it does not require root privileges, Database FlashSnap overcomes these obstacles by enabling database administrators to create consistent snapshots of the database more easily. The snapshots can be utilized for repetitive use.

Database FlashSnap Applications

The following are typical applications of VERITAS Database FlashSnap:

• Database Backup and Restore: Enterprises require 24/7 online data availability. They cannot afford the downtime involved in backing up critical data offline. By creating a clone database or a duplicate volume snapshot of data, and then using it to back up your data, your business-critical applications can continue to run without extended down time or impacted performance. After a clone database or snapshot volume is created, it can be used as a source to back up the original database.
• Decision-Support Analysis and Reporting: Operations such as decision-support analysis and business reporting may not require access to real-time information. You can direct such operations to use a clone database that you have created from snapshots using VERITAS Database FlashSnap, rather than allowing them to compete for access to the primary volume or database. When required, you can quickly resynchronize the clone database with the primary database to get up-to-date information.
• Application Development and Testing: Development or service groups can use a clone database created with Database FlashSnap as a test database for new applications. A clone database provides developers, system testers, and quality assurance groups with a realistic basis for testing the robustness, integrity, and performance of new applications.
• Logical Error Recovery: Logical errors caused by an administrator or an application program can compromise the integrity of a database. You can recover a database by restoring the database files from a volume snapshot or by recovering logical objects (such as tables, for example) from a clone database created from volume snapshots using Database FlashSnap. These solutions are faster than fully restoring database files from tape or other backup media.

Using Database FlashSnap

The system administrator needs to configure storage according to the requirements specified in the snapplan. For information on configuring storage, see Preparing Hosts and Storage for Database FlashSnap.

Database FlashSnap allows you to check the storage setup against requirements set forth in the snapplan. Depending on the results, the database administrator may need to modify the snapplan or the system administrator may need to adjust the storage configuration. Properly configuring storage is the only aspect of using Database FlashSnap that requires the system administrator's participation.

To use Database FlashSnap, a database administrator must first define their snapshot requirements. For example, they need to determine whether off-host processing is required and, if it is, which host should be used for it. In addition, it is also important to consider how much database downtime can be tolerated. Database snapshot requirements are defined in a file called a snapplan. The snapplan specifies snapshot options that will be used when creating a snapshot image (such as whether the snapshot mode will be online, offline, or instant). For further details, see Creating a Snapplan (dbed_vmchecksnap).

After creating the snapplan, the database administrator must validate it to ensure that it is correct. During validation the snapplan is copied to the repository before using it to create a snapshot. Depending on the validation results, the database administrator may need to modify the snapplan or the system administrator may need to adjust the storage configuration.

After storage is configured as specified in the snapplan and the snapplan has been validated, the database administrator can create snapshots of the database and create database clones based on the snapshots on either the same host or a secondary one.

A database clone can be used on a secondary host for off-host processing, including decision-support analysis and reporting, application development and testing, database backup, and logical error recovery. After a user has finished using the clone on a secondary host, the database administrator can shut down the clone and move the snapshot database back to the primary host. Regardless of whether a snapshot is used on the primary or secondary host, it can be resynchronized with the primary database using Database FlashSnap. Database FlashSnap utilizes VERITAS Volume Manager FastResync to quickly resynchronize the changed section between the primary and snapshot. Refer to the VERITAS Volume Manager 4.1 User's Guide for details about the Volume Manager FastResync.

Database FlashSnap can also be used to recover the primary copy of the database if it becomes corrupted by overwriting it with the snapshot. You can recover the primary database with a snapshot using the reverse resynchronization functionality of Database FlashSnap.

Database FlashSnap Commands

The Database FlashSnap feature consists of three commands:

• dbed_vmchecksnap (used on the primary host)

Creates and validates the snapshot plan used to create a snapshot image of an Oracle database. You can also use dbed_vmchecksnap to copy, list, or remove a snapplan or make sure the storage is configured properly for the task. dbed_vmchecksnap is also used on the secondary host to list the snapplan.

• dbed_vmsnap (used on the primary host)

Creates a snapshot image of an Oracle database by splitting the mirror volumes used by the database. You can also use dbed_vmsnap to resynchronize snapshot volumes with their original volumes. The command also allows you to resynchronize the original volumes from the data in the snapshot volumes, which is useful if the original volumes become corrupted. Resynchronizing the original volumes from the snapshot volumes is known as reverse resynchronization.

• dbed_vmclonedb (used on the primary or secondary host)

Mounts and starts a clone database using snapshot volumes. It can also shut down a clone database and deport its volumes, as well as restart a clone database that has been shut down. The snapshot image can be brought up on the same host running the primary database or on a secondary host.

All of these commands can be executed by the Oracle database administrator and do not require superuser (root) privileges.

Database FlashSnap Options

Database FlashSnap offers three options for creating database snapshots. The option you choose is specified in the snapplan.

• online

With this option, the tablespaces are put into online backup mode before the snapshot is created. This type of snapshot is also a valid database backup. Select this option if you are performing a point-in-time recovery from logical errors.

• instant

With this option, the database can be up and running, and the tablespaces do not need to be put into online backup mode before the snapshot is created. However, all the file systems used by the database (including those containing the online redo logs and control files) are temporarily frozen and the cache is flushed before the snapshot is created. By freezing the file systems, the snapshot will be a consistent point-in-time image of the database from which a database clone can be created.

An instant snapshot can be used to guard against data corruption or for off-host decision-support queries. However, it is not a valid database backup and cannot be used to perform a point-in-time recovery or off-host backup since tablespaces are not put into online backup mode before the snapshot is created. The instant option is much faster than the online option.

• offline

The offline option can be used to clone or back up a database. With this option, the database must be shut down when the snapshot is created. and online redo logs are required. This type of snapshot is a valid database backup.

---

  Note    In this release of VERITAS Storage Foundation for Oracle, Database FlashSnap supports third mirror break-off snapshots only. Third mirror break-off snapshots are fully synchronized, full-sized snapshots. See the VERITAS Volume Manager Administrator's Guide for more information.

---