I’ve been doing a bit of work on this, and I wanted to dispel a couple of thoughts I came across regarding this feature that is now available with SharePoint 2013.
I’ve been looking at ways to optimise the Infrastructure required when attempting to upgrade from SharePoint 2010 -> SharePoint 2013.
The wise amongst us would say it’s just a simple case of building out your new SP2013 infra, moving your content databases across and upgrading them.
Two thoughts here
Capex Costs, if you have a SharePoint 2010 estate, multiple farms across the globe the costs of building duplicate infra can be significant.
Data volumes, if you have 10’s of TBytes of content databases, moving them from one set of servers to another takes time and the system needs to be offline.
If you Google around the internet, I’m not going to name any names or provide links etc.. you will find quite a lot of posts on what deferred upgrade is all about.
Some blogs / posts you might find may tell you that deferred upgrade does not modify the SharePoint 2010 schema, hmm I thought that might help me out in terms of not need to completely duplicate the SharePoint infra, I could duplicate the WFE of the SharePoint farm, and then just drop the content DB’s from one farm, add them to the other, and do a deferred upgrade on SP2013, and if something were to go wrong it would be possible to re-attach the DB’s to the old SP2010 farm as a rollback strategy.
After spending a few hours investigating this idea, I have concluded that some of the posts / blogs on the internet are misleading.
If you examine the contents of the dbo.Versions table in a upgraded SP2010 content databases even if you do not carry out the visual upgrade, and choose to leave everything looking like SP2010 (deferred upgrade) the DB schema is definitely changed.
The dbo.Versions table get’s an extra 120+ row’s added to it all with v15+ numbers.
If you then attempt to reconnect this database to an SP2010 farm, it no longer functions, due to schema incompatibly errors.
So just for the record the deferred upgrade definitely modifies the content database schema making it incompatible with SP2010.