This is a very common concern before thinking for a siebel upgrade. As per Anjneya "It does depend on the customization of the older application while doing upgrade.Higher the custom application higher the risk. It is require to more impact analysis while starting the upgrade project ". While Mayank recommends "If the customization is high in legacy then go in for reimplementation rather than upgrade. It also depends upon business criticality fo this application (higher the criticality more the regression you'll need). "
Mahesh Balan has shared his views thoroughly.
Some of the key challenges with an upgrade are
(1) Time it takes to complete it – Regular releases are "frozen" during this time
(2) Deciding on the scope – There is a temptation to try to take advantage of many "new features"
(3) Ensuring that the software and hardware requirements for the upgraded environment are taken into account – Especially 3rd party software compatibility is ignored many times till the last minute
(4) Ensuring upgrade is doable within a downtime window – This requires tuning and practice.
Given the challenges, here are 10 common best practices for upgrades:
• Treat Your Upgrade Activity as a Formal Company Project
• Determine Your Upgrade
• Verify Your Installation & Adhere to Current Minimum Technical Requirements
• Decide When to Change or Add Business Processes
• Utilize skilled, Trained and Experienced Resources
• Train End Users on the New Solution
• Minimize Application Data to Upgrade
• Plan for Upgrade Tuning to Fit Within Your Down Window
• Prepare a Go Live Checklist, and Use IT!
• Perform Mock Production Upgrade Prior to Go-live