HP OpenView Storage Mirroring User Guide (360226-002, May 2004)

11 - 5
How Failure Detection Works
1. The target sends a monitor request, which is an ICMP ping, to each monitored IP address at a user-defined interval. A
monitor reply is sent from the source back to the target.
2. When the user-defined number of missed packets is met, the address is considered failed.
Client Connectivity
Depending on the type of client workstations, the timeout settings, and the applications in use, the clients may notice only a
slight pause while the failover process occurs. If the failover timeout is set to a duration such as several minutes, clients may
see an Abort or Retry message at their machine if they try to communicate with the source before the timeout has expired
and the failover process has completed. For most 32-bit clients and network aware applications, reconnection is automatic.
In the case of older client software, the workstation may need to be rebooted to reestablish a connection to the target, which
is now acting as the source.
Operating System Differences
The source and target machines should be similarly configured (operating system, applications, service packs, patches, and so
on) in order for the applications and services running on the source to be available on the target after failover. Since the
Windows registry should not be replicated between machines, required applications should be preinstalled on the target and
left idle so they do not open or modify replicated files. The pre-failover and post-failover scripts will start required applications.
The following pages detail some of the operating system differences of failover.
Windows 200x
! Storage Mirroring failover can monitor an unlimited number of source machines and can assume the identity of multiple
sources.
! During the failover process the target maintains its original identity and adds the name(s) and IP address(es) of one or
more failed source machines.
! Global unique IDs (GUID) used in Windows 200x are mirrored and replicated to the target machine, stored in an
attribute database, and only set if failover occurs.
! If the identity of the source is added to the target during failover, no services are stopped or restarted.
! The following table describes the source and target configurations of Windows 200x machines that are supported by
Storage Mirroring.
Ta r g e t
Domain Controller Member
Source
Domain Controller
X
a
a. If you are using Active Directory, additional steps are required in your failover and failback scripts to
accommodate Active Directory security.
X
Member
X
Request
Monitor
Request
Monitor
Request
Monitor
Request
Monitor
Request
Monitor
Reply
Monitor
Reply
Monitor
Reply
Monitor
Request
Monitor
Reply
Missed
Reply
Missed
Reply
Missed
Begins
Failover