Shadow set recovery and repair are handled by volume processing,
which replaces mount verification for shadow sets. Membership failure
decisions are made by the VAX hosts. Device errors that result in inaccessibility
of physical member units first utilize the class driver's connection
walking algorithm. If that fails, a local decision is made on the
shadow set membership. The rules are:
If some, but not all, members of the
set are accessible, then the local node sequentially adjusts the membership
and notifies the other hosts.
If no members are accessible, no modifications to
the set membership are made.
There are two types of volume processing: active and passive.
Active volume processing handles error processing on a local node.
Triggered by a failed I/O operation, active volume processing also
controls mount verification functions, member removal, and failover.
Passive volume processing is triggered by lock messages or by a
cluster event. Passive volume processing revalidates shadow set
membership, ensures that the shadow set reflects changes made outside
the shadow set, and handles the following functions:
Member additions from other nodes
Member removals from other nodes
A new node mounting the shadow set
A node dismounting the shadow set
A system crash on a node that has the shadow set
mounted
For more information, refer to the Volume Shadowing for OpenVMS manual.
HP OpenVMS I/O User's Reference Manual
Shadow-Set Virtual Unit Driver
