I have a production Exchange 2013 CU8 environment spread across two Active Directory sites each with their own DAG. Each DAG is a 4-node DAG and each site has 2 CAS servers sitting behind a Windows NLB of SiteEmailNamespace.domain.com. This used to be a single DAG in a single site, and the addition of the second DAG and second site came with it a large amount of Public Folder data and heavy Public Folder users. There are now significant client issues for people accessing these folders.
On the server-side, you can see RPC requests build until a slew of RPC backoffs appear in the Exchange logs. We've enabled logging for RPC throttling, and these backoffs do not appear to be Exchange throttling policy related. Through testings, we've seen that these backoffs coincide with the degraded client experience.
On the client-side, Public Folder browsing takes a very long time. Some users with a lot of Public Folder favorites also have general Outlook performance issues, where just browsing their inbox and composing messages can take 5-20 seconds for each item to load.
This behavior is the same whether the Public Folders live in a mailbox on their site's server or on the cross-site server.
Does anybody have any insight as to what could be causing these RPC backoffs and performance issues? Thanks.