Accomplishing Fallback Support

To invoke fallback support for two databases in a one-primary to one-fallback configuration, follow the steps that are listed below. Only the system administrator (SA) can invoke the fallback feature. Each sp_fallback_ procedure takes only seconds to complete.

To invoke the fallback feature

On the primary server, execute the following steps:
1. Record the designated server svrfallback as the fallback server on the primary server svrprimary and execute the following:
```
exec sp_addserver 'svrfallback' ,'fallback'
```
2. Give the SA on the fallback server the ability to log on as SA on the primary server by executing the following:
```
exec sp_addremotelogin 'svrfallback' ,'sa' ,'sa'
```
On the fallback server, execute the following steps:
1. Record the primary servers to provide fallback support to:
```
exec sp_addserver 'svrprimary'
```
2. Run a simple test to verify that RPC connections are working and execute the following:
```
exec svrfallback...sp_helplogins
```
3. Enroll databases owned by the fallback server for potential fallback support. RPCs are issued to the fallback server. The first parameter value must match a value in sysservers.srvname (not necessarily srvnetname).
```
exec sp_fallback_enroll_svr_db 'svrprimary' ,'DabSales'
exec sp_fallback_enroll_svr_db 'svrprimary' ,'DabProduct'
```
Note The databases DabSales and DabProduct that are being configured for fallback must be on a switchable disk for fallback to work.

To take over a switchable disk

The following steps should be performed each time the fallback server takes over a switchable disk from the primary server and assigns a new drive letter to the disk:

Record that the switchable hard drive seen as "D:" by the primary server will be seen as "H:" by the fallback server:
```
exec sp_fallback_upd_dev_drive 'svrprimary' ,'D:' ,'H:'
  
```
Activate live fallback support for all databases enrolled from that server and execute the following:.
```
exec sp_fallback_activate_svr_db 'svrprimary', '%'
  
```

If the underlying fallback architecture supports registering applications that are launched automatically when the fallback server takes over, then an application (using DB-Library or ODBC) could be written that connects to the fallback server and executes the stored procedures after each disk switchover.

Note If your model database is 1 MB, then a database device of only 1 MB can hold an entire database. To experiment and familiarize yourself with setting up fallback, use a standard 1.44 MB floppy diskette. To activate the fallback server, you can transfer the floppy diskette from the primary server to the fallback server after stopping the primary server.