SCOM installation path: In-place upgrade or side-by-side installation

The day has finally come and it's time to upgrade your Operations Manager deployment. You ask yourself, should I upgrade my existing installation or should I start from scratch and build a new environment, side-by-side?
This is a common question asked by organizations that we work with. To answer this question, we usually begin by asking some simple questions:

• Has your current installation previously been upgraded?
  If your existing environment has already been upgraded, we would recommend considering a clean installation of SCOM. Many things might have been added and removed over the years and it's probably worth the extra work to start fresh.
• What version of SCOM are you running today?
  For the most efficient and seamless upgrade, we recommend upgrading the individual components, one at a time. When we consider which approach to take, it includes life cycle management of all components in the installation, such as the Operating System and SQL Server. Upgrading everything simultaneously could mean downtime and extra work along the way.
• How well is SCOM working today?
  Performance issues, such as excessive alert noise or the presence of unusual errors, can be due to obsolete Management Packs or a misbehaving configuration of SCOM. The misbehavior of your SCOM deployment can be caused by different configuration files or registry settings on your servers. This is a good indication to start over again.
• Is your environment well documented and does it follow strict naming conventions?
  Structure is vital when working with Operations Manager. Many individuals might have been involved over the years, and they might work with different naming conventions when it comes to overrides and groups. In order to correct this, we recommend that you either clean up your existing installation or make sure to follow a new, strict naming convention.
• Does your existing design reflect your current monitoring requirements?
  When your existing environment was installed, the requirements might have been different. Upgrading your environment could be an opportunity to review whether today's requirements are the same or if any roles need to be added or removed.

To aid your decision-making process, we have listed some of the pros and cons:

Side-by-Side Install

Pros (+)

1. Start with a clean slate, no old errors or incorrect configurations are transferred into your new installation.
2. Avoid a big bang upgrade while making the transition to the new installation.
3. Use the latest Operating System and SQL Server supported by SCOM.
4. Test out your integrations in a controlled environment before you go live.
5. Performance impact of Management Packs and workloads are more controlled, and can be monitored along the way as they are implemented.

Cons (-)

1. Data Warehouse history is lost in the old database.
2. Consoles need to be redirected for clients.
3. Firewall rules and backups need to be verified/reconfigured.
4. Added work for multi-homing agents, adding some complexity with Linux Agents.
5. New licenses are needed for third party software due to a new Management Group Name.
6. All configuration files and registry settings need to be reconfigured.

In-place Upgrade

Pros (+)

1. Firewall rules and backups are already working.
2. No need to reinstall and reconfigure Management Packs.
3. Reduces time to implement a new version.
4. Data Warehouse history is retained.
5. No need to multi-home agents.

Cons (-)

1. Higher risk of errors when performing an upgrade, as the procedure is complex and unknown errors could occur.
2. You might still run SCOM on an older version of the Operating System and SQL Server, which requires attention before the actual upgrade. This adds complexity and risk.
3. More downtime is needed when doing the upgrade and preparations.
4. Existing errors and obsolete objects will still remain in your database.
5. Existing performance issues will transition into the upgraded version.

We hope this will help you decide whether to do an in-place upgrade or a side-by-side installation of your new SCOM environment.