Veritas Storage Foundation 5.1 SP1 Cluster File System Administrator"s Guide (5900-1738, April 2011)
■ About Veritas Volume Manager cluster functionality
■ Storage Foundation Cluster File System and Veritas Volume Manager cluster
functionality agents
■ Veritas Volume Manager cluster functionality
About Storage Foundation Cluster File System and
the Group Lock Manager
SFCFS uses the Veritas Group Lock Manager (GLM) to reproduce UNIX single-host
file system semantics in clusters. UNIX file systems make writes appear atomic.
This means when an application writes a stream of data to a file, a subsequent
application reading from the same area of the file retrieves the new data, even if
it has been cached by the file system and not yet written to disk. Applications
cannot retrieve stale data or partial results from a previous write.
To reproduce single-host write semantics, the file system must keep system caches
coherent, and each must instantly reflect updates to cached data, regardless of
the node from which the updates originate.
Storage Foundation Cluster File System namespace
The mount point name must remain the same for all nodes mounting the same
cluster file system. This is required for the VCS mount agents (online, offline, and
monitoring) to work correctly.
About asymmetric mounts
A VxFS file system mounted with the mount -o cluster option is a cluster, or
shared mount, as opposed to a non-shared or local mount. A file system mounted
in shared mode must be on a VxVM shared volume in a cluster environment. A
local mount cannot be remounted in shared mode and a shared mount cannot be
remounted in local mode when you use the mount -o remount option. A single
clustered file system can be mounted with different read/writes options on
different nodes. These are called asymmetric mounts.
Asymmetric mounts allow shared file systems to be mounted with different
read/write capabilities. For example, one node in the cluster can mount read/write,
while other nodes mount read-only.
When a primary mounts "ro", this means that neither this node nor any other
node is allowed to write the file system. Secondaries can only mount "ro", if the
Storage Foundation Cluster File System architecture
About Storage Foundation Cluster File System and the Group Lock Manager
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