| Protect system from server failure |
Use a secondary server that shares disk space
with the primary server. (shared-disk secondary server) |
- Very high availability. This secondary server has access to the
same data as the primary server. If the primary server fails, the
secondary server can take over quickly.
- The database is always in sync because this secondary server has
access to the same data as the primary server.
- No requirement to change applications. Client connections to primary
or secondary server are automatically switched in the event of server
failure.
|
- This secondary server on the same computer as the primary server.
- No data redundancy. This secondary server does not maintain a
copy of the data. (Use SAN devices for disk storage.)
- Primary and secondary servers require the same hardware, operating
system, and version of the database server product.
- Secondary server hardware must be able to handle the same load
as the primary server. If the secondary server is too small, it might
affect the performance of the primary.
|
| Protection from site failure |
- Use a secondary server that maintains a copy of the database server
and the data. (high availability data replication server)
- (Can also use RSS and ER)
|
- Very high availability. Applications can access this server quickly
if they cannot connect to a primary server.
- Data is replicated synchronously.
- Increased scalability
- No requirement to change applications
|
- Local to the primary
- Requires an exact replica of the data (including table and database
schemas).
- Primary and secondary servers require the same hardware, operating
system, and version of the database server product.
|
| Multilevel site failure protection |
- Use a secondary server that is geographically distant from the
primary server and that is updated asynchronously from the primary
server. (remote stand-alone secondary server)
- (Can also use ER)
|
- Very high availability. Applications can access this server quickly
if they cannot connect to a primary server.
- Data is replicated asynchronously.
- Increased scalability
- No requirement to change applications
|
|
| Geographically dispersed processing with site
failure protection |
ER and HDR |
ER and backup for ER |
Multiple connection managers required |