Hi Stuart:
A reboot is needed only when the agent kernel level filter driver (aafsflt.sys) changes and is replaced. In the case of upgrading from the agent software AA 5.4.3 to RR 6.0.x there is a major filter driver change and as such, a reboot is required. Moreover, if you have incompatible anti virus software installed on the Agent (i.e. TrendMicro comes to mind), in some cases you may need to remove the AV software, upgrade the agent and then re-install the AV software. This is needed due to some driver altitude related issues.
Hope that this helps.
I would suggest to look in the logs (c:\programdata\Apprecovery\Logs\Apprecovery.log) to find incompatibility error messages. There is a KB ( support.software.dell.com/.../117506 ) but it is not very specific. I did not work directly with Sophos. In my experience, the newest AV versions comply better with the Microsoft guidelines so, checking if you have the newest version installed is the first step to take. Additionally, you need to attempt the AV exclusions as mentioned in the following KB article support.software.dell.com/.../117680
Basically you want that the RapidRecovery drivers and changelogs are not encumbered by the AV drivers as they may not be able to keep up with the data transfer rates.
On the practical side, as a best practice, I would upgrade an agent installed on a non-production machine and see how it behaves. If no unexpected base images are taken and the snapshots are not slowed down, I would proceed with the update. Since RapidRecovery still works with older agent software, I would do the upgrade over time to make sure that no unforeseen issues occur (and address them if they do) and ensure a "soft landing". Goes without saying that, despite low risk levels, DataProtection should not be treated lightly and, when in doubt, the best thing to do is opening a ticket with our support team :)
