La decisione di migrare a Sql Server 2008 da una versione precedente (2000, 2005) comporta una prima scelta fondamentale : Upgrade in-place (l'istanza viene aggiornata a Sql Server 2008) o side-by-side (viene creata una nuova istanza sullo stesso server o su un server differente e poi gli oggetti vengono copiati manualmente nella nuova istanza). Nella tabella seguente trovate la lista dei vantaggi di entrambe le scelte e in fondo al post il link al documento che oltre alla tabella contiene tutte le informazioni necessarie di cui tenere conto per l'upgrade. Insieme al Books on line costituisce una risorsa fondamentale da tenere in considerazione se vi trovate in fase di pianificazione di un upgrade.

 

Consideration

In-Place Upgrade Advantages

Side-by-Side Upgrade Advantages

Require the fewest hours for the upgrade deployment team to plan and prepare the upgrade effort

·        Setup automatically upgrades data and settings in place, without the need for a manual transfer of data or settings.

·        The resulting upgraded instance has the same name as the original.

·        Applications continue to connect to the same instance name.

·        It gives more granular control over which database objects are migrated.

·        The legacy database server can run alongside the new server. You can perform test migrations and research and resolve compatibility issues without disturbing the production system.

·        The legacy database server remains available during the migration, although it cannot be updated for at least the time that is required to transfer data.

·        Applications can be moved from legacy system in a staged manner instead of all at the same time.   Even though your system might have passed all validation and acceptance test, a problem could still occur (see Murphy’s Law).  If a problem does occur, then you will be able to roll back to the legacy system.

Require minimal DBA skill set expertise (or no DBA available to implement the upgrade)

A junior DBA or System Engineer or similar with basic knowledge and adherence to good IT practices can complete upgrades without special scripts or manual interventions; Setup automates the upgrade process.

System recovery:  If a junior DBA or anybody who is not familiar with the upgrade process has any problems, the production environment remains untouched.  Only when the new system is approved by Test / QA will the users be migrated to the new server.

Require minimal user downtime

For small data sets, the total end-to-end time might be smaller because this is the most automated upgrade strategy.

By controlling the steps directly, you can do much of the preparation including much of the data transfer can be completed without user downtime; some user downtime is still required to update the instance version.

Require fastest possible revert/rollback in case issue encountered

 

The legacy instance of SQL Server is still present at the end of the upgrade and may be used as a rollback option.

Schedule different downtime windows for different user databases within the same instance

 

Can separately control when each user database is upgraded; after the last user database is upgraded, the legacy instance can be removed.

Preserve the Server and Instance name

Preserves the same server and instance name.

 

Server consolidation project

 

The upgraded instance can be placed upon the consolidation server, after which the old server can be taken out of service.

Applications required to run in parallel with the original and new instances of SQL Server

 

Can maintain both systems with production transactions until ready to turn off the original system.

New server hardware or  operating system

 

The upgraded instance can be put upon the new server, after which the old server can be taken out of service.

Shortage of disk space in production

Because there is only one resulting instance, there is less additional dataspace required than is possible with two complete resulting instances running side by side.

 

Legacy Server cannot meet the SQL Server 2008 Setup requirements for installation

None - not supported .

Only possible with side-by-side upgrade to a new server which meets setup requirements.

Changing to a earlier edition of SQL Server 2008

None - not supported.

Only possible with side-by-side upgrade.

Upgrade a 32-bit version of SQL Server 2000 or 2005 to a 64-bit version of SQL Server 2008

None - not supported .

Only possible with side-by-side upgrade.

Upgrade a 64-bit version of SQL Server 2000 or 2005 to a 32-bit version of SQL Server 2008.

None - not supported.

Only possible with side-by-side upgrade.

Target instance is SQL Server 2000 SP3a and only one downtime window is available

 

Transferring data to a new instance may be faster than the two steps required to apply the required SQL Server 2000 SP4 and then upgrading to SQL Server 2008.

Upgrading from a nonclustered legacy instance of SQL Server to a clustered instance of SQL Server 2008

None - not supported.

Only possible with side-by-side upgrade.

Upgrading from SQL Server 7.0

None - not supported; would need first to upgrade to SQL Server 2000 or 2005.

Can be done in one direct upgrade by using manual data transfer.

Upgrading multiple instances

Generally faster because data transfer and configuration steps are handled by Setup.

 

Upgrading very large databases (VLDBs)

Setup converts existing data files automatically; no data transfer steps are required.

Can control the timing of several steps and also the rollback if it is necessary.

Upgrade Testing

 

Re-testing might be easier because the legacy instance of SQL Server does not have to be rebuilt.

Testing can be done while legacy system still supports production applications.   SQL Server Profiler can be used to capture SQL commands against the legacy system and used to play back against the new instance of SQL Server to verify that everything is working well.

Data must be transformed during the upgrade window

 

Data transformation tools such as SSIS can be used to transform data as it is being transferred from the legacy instance of SQL Server to SQL Server 2008.

Localization: change of SQL Server language

 

Enables upgrade to SQL Server 2008 with a different language from the legacy instance of SQL Server. Note: this issue is not to be confused with collation settings. This applies to the localized language of the SQL Server product.

Upgrading Notification Services

None - not supported.

Only possible with side-by-side upgrade. Requires Notification Services backward compatibility add-in.

Application integration

Simpler because the same server name, instance name, and database security settings are preserved by Setup, without manual intervention.

Applications can be moved from legacy system in a staged manner instead of all at the same time. Even though your system might have passed all validation and acceptance test, a problem could still occur. If a problem does occur, then you will be able to roll back to the legacy system.

Server Integration

Might be simpler because linked server, replication, and log shipping settings can be preserved, depending on the SQL Server version being upgraded.

 

 

Sql Server 2008 Upgrade Technical Reference Guide : http://www.microsoft.com/downloads/details.aspx?FamilyID=66d3e6f5-6902-4fdd-af75-9975aea5bea7&displaylang=en