[OpenAFS] mixing AFS versions for db servers?

[Coy Hile]

On Sat, Oct 22, 2011 at 12:18 AM, Jeffrey Altman
<jaltman@secure-endpoints.com> wrote:
> Database servers all must be the same version.
> You can run 1.4.7 database servers on the 1.6.x fileserver machine but
> all of the database servers must match. =A0Mixed versions are not support=
ed.
>

Out of curiousity (as I'm sure I'll come across it soonn enough after
I rebuild my cell), if all dbservers must run the same version, what
is the supported process for updating dbservers?  Certainly if you did
"yum upgrade list-of-openafs-packages" on all three and rebooted them
simultaneously, you'd have an outage -- however short it may be.