[cisco-voip] CallManager Subscriber - How long can it be down

[Carter, Bill]

I got a very interesting hypothetical question from a customer.  

They have 2 CallManager Clusters (cluster A and Cluster B) and want to
purchase 1 more CallManager Server.  They are exploring the options of
having the additional server be a disaster recovery type CallManager for
both clusters.  Obviously 1 server can't be a member of 2 clusters.

They are considering having 2 sets of hard drives for the DR server.
With hard drives A, a DR CallManager Subscriber will be built for
Cluster A.  Hard drives B will be used for a DR CallManager Subscriber
for Cluster B.  

Under normal operations the neither DR CM subscriber will be
operational.  On a daily basis hard drive set A and B will be powered up
to insure CM database synchronization.  For both Clusters Device Pools
etc. will be configured so DR subscriber is the 2nd server.  If a
Publisher CM fails, the DR Subscriber will be powered up with the
appropriate hard drives.

My primary concerns are with the stability of the CM database if a
Subscriber is off-line for an extended period of time.  If the
subscriber is powered off for days or weeks what issues might be
present.  I know there would be problems if configuration changes are
made on a Publisher, they will not be replicated until the subscriber is
on-line.

What other problems might occur?