Preventing Database Tier Failures
You can make the database tier more resilient by using a combination of disk redundancy and a sound backup and restoration strategy to protect your data. You can use any of the following methods to make database services more resilient:
- Clustering. In Windows Clustering, two or more servers can share common data and work together as a single system. Windows Datacenter Server supports up to four servers (nodes) in a cluster. Each node can operate independently of the others.
- Replication. You can use SQL Server replication to synchronize your database servers. SQL Server offers replication options such as snapshot replication and transactional replication. Active Directory also uses replication to ensure redundancy.
- Warm backups. You can use a single production server to provide read/write access to data, logging all transactions. You then use SQL Server log shipping to transfer files to a non-production server that is continuously updated with the transaction log files.
Data must be backed up or replicated to prevent it from being accidentally deleted. The following table describes the two types of data replication.
| Type of data replication | Characteristics | Use when |
|---|---|---|
| Active | Shares a part of the workload of the primary site and is always online. | Data is extremely critical and the site must always be available. |
| Passive | Inactive until a disaster takes the primary site out of operation. | Your site can tolerate brief interruptions in data availability while the backup site comes online. |
Database Connections
Commerce Server and its dependencies use database connections to connect to databases. Since database servers run on top of platform OS and services, the causes of failure are many, including:
- File Disk system crash
- Network failure
- Database application failure
- Server failure
There are two recommended Windows 2000 high availability solutions:
- MSCS Cluster service. This solution is applicable to database servers in publisher mode.
- Network Load Balancing. This solution is applicable in scale-out mode. In this mode, multiple database servers are load balanced under a single virtual IP. The database servers typically function as subscribers to a master database server acting as data publisher. When a database server fails, NLB removes the server from the cluster and directs connections to remaining functional servers.
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