I came across an interesting article today outlining the fact that in SCCM 2012 the CAS always has a copy of all content in the heirarchy, even though clients don’t access the CAS and you can’t deploy the DP role to it. Some extracts from the article:
A lot of people don’t realise that we actually have an SCCMContentLib on our CAS, even if we don’t have a DP on that site system. The SCCMContentLib on a CAS is used a little differently. It isn’t there for clients to access content, is there for Distribution Points to access content. So when I added an OSD WIM image to a DP, it’ kicked off the local processing of the WIM into the local SCCMContentLib.
The key takeaways are, even though you don’t have a DP on your CAS – make sure that you have enough storage to hold EVERY package that will be in your environment (even packages added directly at child primaries) and that your disks are fast enough to allow processing of every package added to SCCM.