VERITAS Storage Foundation 4.1 Cluster File System HP Serviceguard Storage Management Suite Extracts, December 2005

About CFS
56 Installation and Administration Guide
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CVM
The VERITAS Volume Manager cluster functionality (CVM) makes logical volumes
accessible throughout a cluster. CVM enables multiple hosts to concurrently access the
logical volumes under its control. A VxVM cluster comprises nodes sharing a set of
devices. The nodes are connected across a network. If one node fails, other nodes can
access the devices. The VxVM cluster feature presents the same logical view of the device
configurations, including changes, on all nodes. You configure CVM shared storage after SG
sets up a cluster configuration.
About CFS
SFCFS uses a master/slave, or primary/secondary, architecture to manage file system
metadata on shared disk storage. The first node that mounts is the primary node and the
remaining nodes are secondaries. Secondaries send requests to the primary to perform
metadata updates.The primary node updates the metadata and maintains the file system’s
metadata update intent log. Data can also be updated from any node directly to shared
storage. Other file system operations, such as allocating or deleting files, can originate
from any node in the cluster.
If the server on which the SFCFS primary is running fails, the remaining cluster nodes
elect a new primary. See “Distributing Load on a Cluster” on page 60 for details on the
election process. The new primary reads the file system intent log and completes any
metadata updates that were in process at the time of the failure. Application I/O from
other nodes may block during this process and cause a delay. When the file system is
again consistent, application processing resumes.
Because nodes using a cluster file system in secondary mode do not update file system
metadata directly, failure of a secondary node does not require metadata repair. SFCFS
recovery from secondary node failure is therefore faster than from primary node failure.