HP StorageWorks Storage Mirroring application notes Guidelines for networking and failover (T2558-96063, February 2008)

infrastructure. The following information, at a minimum, is required in order to design the failover

configuration:

• Which clients will be accessing the failed-over server?

• What are the client, source, and target operating systems?

• Where are the clients and target located?

• What are the name resolution method of clients?

• What is the WINS configuration of clients and target?

• What is the DNS configuration of the clients?

• What is the WINS architecture?

• What is the DNS architecture?

• What type of domain is in use (Windows NT or Active Directory)?

• Where are the Active Directory domain controllers located?

• In what container is the source's Active Directory computer account?

A failover solution may work in a test environment but fail in production if not properly designed, and the

information listed above is required in order to design it properly. Until the solution is properly designed,

actions taken to resolve a specific issue may appear to have resolved an issue when in fact they were

irrelevant. For example, if a Windows NT 4.0 client is using a WINS server that did not get updated at

failover, it will not be able to access the failed-over server until its WINS server receives replication from the

target's WINS server. If the Storage Mirroring service account is changed and failover is tried again, the

client may be able to access the failed-over server, not because of the change that was made, but because

the WINS replication finally occurred just before failback. Accordingly, a “shotgun” approach to resolving

issues may lead to false conclusions, confusion, and extended troubleshooting time.

In general, failure to update WINS servers and SPNs are the most common causes of client access issues

after failover. If the client or target is not Windows 2000 or later, then the issue is most likely failure to

update WINS servers. If the client and target are Windows 2000 or later, then the issue is most likely

failure to update SPNs.

After the correct configuration has been determined and verified, troubleshooting should begin with

verifying that the IP address and name were failed over correctly. This can be done by running the

following two commands:

Nbtstat -n

IPConfig /all

Caches containing MAC address, NetBIOS, and DNS host names have not been known to cause any

issues with client access and flushing the caches will not resolve the issue. In general, if the requested

operation fails, the operation is retried without using the cached entry. Viewing the cached entries is

usually only relevant to finding out what the name resolution servers are returning.