NetVault Plug-in for SQL Server 12.0 - User Guide

Restoring data

Restoring data: an overview

Restoring is the process of copying data from a backup and applying transaction logs to the data to roll it forward to the target recovery point. A backup contains sufficient transaction log records to allow rolling forward the active transactions as part of restoring each backup. Each backup also contains sufficient transaction logs to roll back any uncommitted transactions to bring the database to a consistent, usable state. The process of rolling forward uncommitted transactions, if any, and bringing the database online is known as Recovery.

NOTE: If your SQL Server Database Security Administrator or DBA has enabled Transparent Data Encryption (TDE) for one or more SQL Server Databases, then before restoring a TDE enabled database, SQL Server Database Security Administrator, or DBA must restore required TDE certificate on the SQL Server target instance.

This topic includes the following subtopics:

Reviewing the phases of the VDI restore sequence

Each SQL Server restore scenario is implemented using one or more restore operations, which is called a restore sequence. A restore sequence moves data through one or more phases of restore. The possible phases of a restore include the data copy, redo (roll forward), and undo (roll back) phases, which are detailed in the following topics.

The first phase in any restore process is the data copy phase. The data copy phase involves copying all the data, log, and index pages from the backup media to the database files. It involves copying data from one or more of the following backup types:

Redo is the process of reapplying logged changes to the data in the roll-forward set to bring the data forward in time. To accomplish the redo, the SQL Server Database Engine processes Transaction Log backups as they are restored. The engine starts with the log contained in the data copy backups listed in the preceding topic and any Incremental Transaction Log backups that are then restored. Roll forward stops at the recovery point; this point is either the end of the log or a point specified in the SQL Server restore options for Incremental Transaction Log backups. Plug‑in for SQL Server supports both time-based and marked transaction-based PIT recovery.

After the redo phase has rolled forward all the log transactions, a database typically contains changes made by transactions that are uncommitted at the recovery point. This result makes the rolled forward data transactionally inconsistent. The recovery process opens the transaction log and identifies uncommitted transactions and rolls them back to bring the database into a transactionally consistent state. This step is called the undo phase.

If the data is transactionally consistent at the start of the recovery process, the undo phase is skipped.

After the database is transactionally consistent, recovery brings the database online.

Understanding the available types of Online VDI restores

To perform a successful restore, you must have a full understanding of the types of restores that are available for use. This topic outlines the possible restore scenarios supported for different recovery models.

The following restore scenarios are supported under Simple Recovery Model:

The following restore scenarios are supported under the Full and Bulk-Logged Recovery Models: