From my experience DP9 is far from being stable.
Did a new Installation in December with v9.02 and took us 2 Business Escalations and around 2 dozen Hotfixes to somewhat get the Env running stable in May (around 30 Windows/Linux Clients, Exchange 2013, MSSQL, VMware).
If you can, do a clean install on a new CellServer and slowly migrate your Clients and long-term media over.
Even with many improvements to the Upgrade-Process over the last Patchbundles it is still very tricky and prone to errors.