Designing Disaster Tolerant High Availability Clusters, 10th Edition, March 2003 (B7660-90013)

Building a Metropolitan Cluster Using MetroCluster/CA

Maintaining a Cluster that uses MetroCluster/CA

Chapter 3114

• Failure of the secondary XP Series disk array for a given application

package followed by application startup on a primary host

• Failure of all CA links with Fence Level NEVER and ASYNC with

restart of the application on a primary host

Using the pairresync Command

The pairresync command can be used with special options after a failover

in which the recovery site has started the application and has processed

transaction data on the disk at the recovery site, but the disks on the

primary site are intact. After the CA link is fixed, you use the

pairresync command in one of the following two ways depending on

which site you are on:

• pairresync -swapp—from the primary site.

• pairresync -swaps—from the failover site.

These options take advantage of the fact that the recovery site maintains

a bit-map of the modified data sectors on the recovery array. Either

version of the command will swap the personalities of the volumes, with

the PVOL becoming the SVOL and SVOL becoming the PVOL. With the

personalities swapped, any data that has been written to the volume on

the failover site (now PVOL) are then copied back to the SVOL now

running on the primary site. During this time the package continues

running on the failover site. After resynchronization is complete, you can

halt the package on the failover site, and restart it on the primary site.

MetroCluster will then swap the personalities between the PVOL and

the SVOL, returning PVOL status to the primary site.

NOTE The preceding steps are automated provided the default value of 1 is

being used for the auto variable AUTO_PSUEPSUS. Once the CA link

failure has been fixed, the user only needs to halt the package on the

recovery cluster and restart on the primary cluster. However, if you want

to reduce the amount of application downtime, you should manually

invoke pairresync before failback.