Availability figures are commonly calculated based on the time the system has been operating satisfactorily. This commonly does not include planned outages because we can foresee them and plan around them, i.e., move the required Service to another node in our cluster. In this way, the overall availability of the Service that a system provides has not been affected, even though the individual system has been down. Commonly, users are not concerned about individual systems but overall application/service availability.
A2:
The Annualized Failure Rate is calculated by taking:
Hence the AFR for my tape drive =
This equates to 2.2 failures per device per year. For 10 tape drives , we would expect 22 failures per year.
A3:
The additional security features that HP-UX Trusted Systems offers can be used to secure and monitor individual hosts . From a purely high-availability perspective, this is good insofar as we need to ensure that a single node is not compromised, and if so, we know about it as soon as possible. From a clustered viewpoint, HP-UX Trusted Systems offer a challenge insofar as ensuring that usernames and passwords are consistent across the entire cluster. Currently, HP-UX Trusted Systems cannot be integrated with an LDAP Directory Server, although it can be integrated into an NIS+ environment.
A4:
Yes. PC clients should support dynamic routing because a router in itself can be seen as a Single Point Of Failure in a high-availability network. By utilizing dynamic routing, the user PCs can have their routing tables updated with a new default route when necessary. The Router Discovery Protocol is sufficient in a small- to medium- sized network. However, we will need to ensure that the PC client operating system supports RDP and ICMP redirects.
A5:
This not a valid ServiceGuard cluster because a data/heartbeat LAN and a Standby LAN must be part of the same network and connected via a hub/switch. The use of a router to connect two segments of the same subnet is not a valid configuration.
