Introduction

In this article, I would like to emphasize more on the types of data you backup in your organization and what options do we have and why we use those options in different scenarios.

Backing up and recovering Exchange data is a bit different than backing up other types of data, primarily because Exchange has different units of backup and recovery than Microsoft Windows. You not only work with files and drives, you also work with the information store and the data structures it contains. Remember, the information store can contain one or more storage groups and in turn, each storage group can contain one or more databases.

What makes a complete backup of an Exchange Server?

• Exchange configuration data, which includes the configuration settings for the Exchange organization. You take the configuration settings from the Exchange directory database (Dir.edb), Active Directory, the Windows registry, and the Key Management Service database, if installed. Configuration data does not include any user data.
• Exchange user data, which includes Exchange mailbox store databases, public folder store databases, and transaction logs. User data does not contain Exchange configuration settings.
• System state data for the operating system, which includes essential system files needed to recover the local system.
• Folders and drive that contain Windows and Exchange files.

Storage groups and databases are the units of backup and recovery for the information store. Storage groups are the smallest units of backup, and mailboxes are the smallest units of recovery. In other words, you have the following backup and recovery options for the information store.

Backup Options – You can backup the following:

• entire information store.
• backup sets of storage groups
• individual storage groups

Recovery Options – You can recover the following:

• entire information store.
• sets of storage groups
• individual storage groups
• groups of databases
• individual databases
• individual mailboxes

Exchange 2000 and 2003 has greater ability to recover an individual database from backup compared to Microsoft Exchange 5.0 and Exchange 5.5. There are some fundamental issues about transactions we all should know before recover individual databases such as transactions, transaction logs, and transaction logging modes.

Exchange server uses transactions to control database changes. Imagine transaction as a logical unit of work that contains one or more operations that affect the information store. If all the operations in a transaction are successfully executed, Exchange Server marks the transaction as successful and permanently commits the change. Otherwise, marks the transaction as failed and removes any changes that the transaction created – this process is called rolling back.

Transactions logs are the units of storage for transactions. Exchange Server writes each transaction to a log file and maintains the log files according to the logging mode.

Following are the two transaction logging modes:

Standard – Using standard logging, Exchange server reserves 5 MB of disk space for the active transaction log. As soon as the contents of the log reach 5 MB, Exchange server creates new log file. Remember, the transaction logs are kept until the next Full Backup, and you recover Exchange Server to the last transaction.

Circular - Circular logging works much like standard logging with one key distinction. Exchange server overwrites transaction log files after data they contain has been committed to the database. This method reduces Exchange Server disk space requirements. The drawback is, Exchange Server cannot recover to the last transaction without old transactions logs which results Exchange server to recover only up to the last Full backup.

The ability to recover mailboxes selectively from backup is an improvement over Microsoft Exchange 2000. Recovery Storage Groups (RSG) is special types of storage groups that are reserved for recovery operations. You use RSG to restore mailboxes from any of the regular storage groups in an Exchange organization. You can recover individual or multiple mailboxes at the same time, provided the database for those mailboxes is in the same storage group. RSG cannot be used to restore public folder databases.

Note: The server on which you create recovery storage group must be in the same administrative group as the server for which you want to recover mailboxes. If you need to recover mailboxes stored on multiple Exchange servers, you don’t have to create a recovery storage group on each server. Instead, you can create one recovery storage group for each administrative group.

Choosing Backup Options

You can perform backups online (while exchange services are running) or offline (while exchange services are stopped). With online backups, you can archive the following items:

• Exchange configuration data
• Exchange user data
• System state
• Files and folders that contain Windows and Exchange files.
  

With offline backups, you are not able to archive Exchange configuration or user data. In other words, you can only archive the following items:

• System state
• Files and folders that contain Windows and Exchange files.
  

Here are the basic types of backups you may want to perform:

• Normal/Full Backup – Backs up all Exchange Data that has been selected, including related data stores and current transaction logs. Once backup complete, it clears out the transaction logs.
• Copy Backups - Backs up all Exchange Data that has been selected, including related data stores and current transaction logs. Unlike a normal backup, this type of backup won’t tell Exchange Server that you have performed complete backup, resulting unclear transaction log files.
• Differential Backup – Designed to create backup copies of all data that has changed since the last normal backup. Only transaction log files are backed up and not the actual data stores. The log files are not cleared. Meaning, to recover Exchange server, you need most recent normal backup and most recent differential backup.
• Incremental Backup – Designed to create backups of data that has changed since the most recent normal or incremental backup. Only transaction log files are backed up and not the actual data stores. The log files cleared as soon as Incremental backup is completed. To recover Exchange server, you need the most recent full backup and then apply each incremental backup after the full backup and must apply transactional logs in order.

Important Note: You cannot perform incremental or differential backups with circular logging enabled because circular logging allows Exchange server to overwrite log files, which makes it impossible to reliably restore from transaction logs.

As a best practice, you may want to plan your backup in such a way that to perform full backups on a weekly basis and supplement them with nightly differential or incremental backups. Also carefully plan the tape rotation and off-site storage.