Strategies for disaster protection

IBM Spectrum Protect™ provides strategies to protect data if a disaster occurs. These strategies include node replication to a remote site, storage pool protection, database protection, and device replication to a standby server.

Replication to a remote site

Replication is the process of incrementally copying data from one server to a remote server. The server from which client data is replicated is called a source replication server. The server to which client data is replicated is called a target replication server. A replication server can function as a source server, a target server, or both. You use replication processing to maintain the same level of files on the source and the target servers. Figure 1 shows the node replication process to a remote site.

Figure 1. Node replication process
Illustration shows the node replication process

When client data is replicated, data that is not on the target server is copied. When replicated data exceeds the retention limit, the target server automatically removes the data. To maximize data protection, you synchronize the local server and the remote server, for example Site B replicates data from Site A and Site A replicates data from Site B. As part of replication processing, client data that was deleted from the source server is also deleted from the target server.

IBM Spectrum Protect provides the following replication functions:
  • You can define policies for the target server for the following conditions:
    • Identical policies to the source server
    • Different policies to cater for different business requirements
    If a disaster occurs and the source server is unavailable, clients can recover data from the target server. If the source server cannot be recovered, you can convert clients to store data on the target server. When an outage occurs, the source server can automatically fail over to a target server for data recovery.
  • You can use replication processing to recover damaged files from FILE or DISK storage pools. You must replicate the client data to the target server before the file damage occurs. Subsequent replication processes detect damaged files on the source server and replace the files with undamaged files from the target server.

Role of replication in disaster protection

If a disaster occurs, you can recover replicated data from the remote site and maintain the same level of files on the source and target servers. You use replication to achieve the following objectives:
  • Control network throughput by scheduling node replication at specific times
  • Recover data from large-scale site loss
  • Recover damaged files on the source server

To ensure a high level of server availability, you can use replication with a group of servers and clients, in other words clustering. In a clustered environment, a client is less likely to fail over to another server. If you replicate data from several source servers to one target server, you create a high dependency on the target server. A clustered environment reduces the dependency on the target server.

Storage pool protection

You use different techniques to protect against the permanent loss of data that is stored in directory-container storage pools and in FILE and DISK storage pools.

Directory-container storage pools

You use storage pool protection to protect specific directory-container storage pools if you do not need to replicate all the data that is contained in a client node. By protecting a directory-container storage pool, you do not use resources that replicate existing data and metadata, which improves server performance.

For best data protection, protect the directory-container storage pool before you replicate the client node. When node replication is started, the data extents that are already replicated through storage pool protection are skipped, which reduces the replication processing time. You can repair specific directory-container storage pools.

Container-copy storage pools

You use container-copy storage pools to protect directory-container storage pools by copying the directory-container storage pool data to tape volumes. Use container-copy storage pools to create up to two tape copies of a directory-container storage pool. The tape copies can be stored onsite or offsite. Damaged data in directory-container storage pools can be repaired by using container-copy storage pools. Container-copy storage pools provide an alternative to using a replication server to protect data in a directory-container storage pool.

Storage pools that are associated with FILE and DISK device classes

You use node replication to protect storage pools that are associated with FILE and DISK device classes. When you restore a storage pool, the server determines which files are in that storage pool. Using file copies from a copy storage pool or an active-data storage pool, the server restores the files to the same or a different storage pool. As part of a restore operation, inactive file versions are deleted from the server database. Inactive file versions are deleted if the server determines that an inactive file needs to be replaced but cannot find the file in the active-data pool.

Database protection

You can use the replication technique to protect against the permanent loss of data that is stored in the server database. The database backup can be full, incremental, or snapshot. To restore the database, you must have the backup volumes for the database. You can restore the database from backup volumes by either a point-in-time restore or a most current restore operation.

Point-in-time restore
The point-in-time restore operation includes the following actions:
  • Removes and re-creates the active log directory and archive log directory that is specified in dsmserv.opt file.
  • Restores the database image from backup volumes to the database directories recorded in a database backup or to new directories.
  • Restores archive logs from backup volumes to the overflow directory.
  • Applies logs from the overflow directory up to a specified point in time.
Most current restore
The most current restore operation includes the following actions:
  • Does not remove and re-create the active log directory or archive log directory.
  • Restores a database image from the backup volumes to the database directories recorded in a database backup or to new directories.
  • Restores archive logs from backup volumes to the overflow directory.
  • Applies logs from overflow directory and archive logs from archive log directory.

Use point-in-time restore operations for situations such as disaster recovery or to remove the effects of errors that can cause inconsistencies in the database. Restore operations for the database that use snapshot backups are a form of point-in-time restore operation. If you want to recover the database to the time when the database was lost, recover the database to the most current state.

Alternative methods for disaster protection

In addition to replication to a remote site, you can also use the following methods to protect data and implement disaster recovery with IBM Spectrum Protect:
Sending backup tapes to a remote site
Data is backed up to tape at scheduled times by the source server. The tapes are sent to a remote site. If a disaster occurs, the tapes are returned to the site of the source server and the data is restored on the source clients.
Multisite appliance replication to a standby server
In the multisite appliance configuration, the source appliance is replicated to a remote server in a SAN architecture. In this configuration, if the client hardware at the original site is damaged or destroyed, the source device can be replicated from the standby server at the remote site. This configuration provides disk-based backup and restore operations.