Although Microsoft released SharePoint 2016 many months ago, there are still some companies out there which are using older SharePoint versions (like SharePoint 2007 or SharePoint 2010). A SharePoint migration from an older version of SharePoint (like SharePoint 2010 or SharePoint 2007) to an up-to-date version of SharePoint (like SharePoint 2016 or SharePoint online) is not an extraordinary process. If content from an older version of SharePoint is to be migrated to SharePoint online, there are some things that should be considered, before starting the migration.
1. Pre-Migration Assessment
Although a pre-migration assessment usually is an important part of the pre-migration planning, it becomes more important, if content from an older version of SharePoint needs to be migrated. A pre-migration assessment is helpful to find out if the selected migration tool can migrate content and settings faultlessly. Usually, the log files of a pre-migration assessment provide valuable hints which list, library, or web part might cause problems during the migration. I recommend doing a pre-migration assessment as it is needed to plan the migration process thoroughly.
2. Review site and subsite structure
With SharePoint 2007 it was common to create the site structure similar to the structure of the organization. In other words: the site structure in SharePoint was reflecting the organization's structure one to one. At that time this was the usual approach, but today a site structure does not reflect the structure of the organization anymore. Instead, structures are reflecting internal procedures or are focusing on department-comprehensive projects. In other words: today's site structures are user-centric and are based on processes and internal collaboration rather than copying the internal structure of an enterprise.
That's the reason why the site structure of an older SharePoint farm needs to be reviewed very thoroughly. In most cases, it makes sense to create a kind of mapping table for sites and subsites. This mapping table lists all the sites and subsites in the old portal and describes how this translates to the new site structure in SharePoint online.
3. Review existing business applications
Although SharePoint 2007 was not used as a platform for integrated business applications like newer versions of SharePoint, many companies created what I like to call 'Mini Applications'. Those mini applications are not based on custom code, but on joined lists with lookup fields, content types, and sometimes calculated fields. Some enterprises created very complex structures by just using multiple generic lists which are joined by lookup fields. The problem with that kind of applications is, that they have been used for many years and that employees have become accustomed to them.
While these applications can be migrated to SharePoint without major issues, it makes sense to check, if these applications can be updated or modernized before migrating them. Sometimes a SharePoint-hosted add-in (which wasn't available to previous versions of SharePoint) can be used to replace some functionality and to improve the usability. If a mini application is frequently used, it can be beneficial to rethink its internal structure and use-case to see if it can be replaced by a SharePoint-hosted add-in or a Provider-hosted add-in.
4. Review branding
If you compare the out-of-the-box branding of SharePoint online with the out-of-the-box branding of SharePoint 2007, you'll notice a huge difference - and that's true for the user interface as well. If a company has invested a significant effort in creating a corporate SharePoint branding and wishes to migrate this, it will be problematic. Due to the massive changes in SharePoint online compared to SharePoint 2007, an old SharePoint 2007 branding can't be migrated to SharePoint online completely. My recommendation is to take the old SharePoint 2007 branding as a basis and create a new corporate branding for SharePoint online which is adapting the modern user interface of SharePoint online in a beneficial way but still looks similar to the old branding.
5. Review the size of lists and libraries
At the times when SharePoint 2007 was popular, there was no such thing as a 5000-items limit like it exists in SharePoint online today. As a result many enterprises created generic lists which contained over 5000 items, which resulted in a decreased performance, but still worked.
While these large lists can be migrated to SharePoint online, problems will occur as soon as these lists have been migrated to SharePoint online. If a view is returning more than 5000 items, SharePoint online is displaying an error message.
If there are lists with several thousands of items in the old SharePoint farm, I highly recommend reviewing those lists before migrating them. Sometimes the problems can be solved by creating additional filtered views which are based on indexed columns. Sometimes it makes more sense to split up those large lists into multiple lists based on particular topics or to create annual lists.
6. Plan timelines thoroughly
Migrations are usually done with the help of tools (like ShareGate or Metalogix). If these tools are used to migrate content from SharePoint on-premises to SharePoint online, these tools need to utilize the Client-side API which is significantly slower compared to the popular and powerful SharePoint Server-side API. The Client-side API is not the only factor which affects the time needed to migrate content and settings to SharePoint online. The varying performance of Office 365 and the throughput rate of the internet connection used during the migration can also affect the duration of the migration. To get some basic time estimates, a look at the reports of the pre-migration assessment can be helpful as they include information about the amount of data and throughput rates.
7. Prepare user training
As I have mentioned earlier, the user interface of SharePoint online has been changed dramatically compared to SharePoint 2007. Although the basic functionality (like adding items to a list or updating the metadata of a document) still exists in SharePoint online, the way that functionality is exposed through the user interface has been changed considerably. Without an aligned user training, the user acceptance of the new SharePoint online portal will suffer significantly simply because the employees feel confused or overwhelmed by the new user-interface.