HP StorageWorks Clustered File System 3.6.0 Windows Storage Server Edition Administration Guide (403103-005, January 2008)

Chapter 9: Configure PSFS Filesystems 95
Filesystem Management and Integrity
HP Clustered File System uses the SANPulse process to manage PSFS
filesystems. SANPulse performs the following tasks.
• Coordinates filesystem mounts, unmounts, and crash recovery
operations.
• Checks for cluster partitioning, which can occur when cluster network
communications are lost but the affected servers can still access the
SAN. If this situation occurs, HP Clustered File System determines
which servers should continue to have SAN access and excludes the
other servers from the SAN. This step prevents data corruption from
occurring.
• Communicates filesystem status to the HP CFS Management Console.
It reports both the global status of a filesystem (for example, whether
it is up or going through a recovery operation) and the status of the
filesystem on each server (for example, whether the filesystem is
mounted or unmounted).
Filesystem Synchronization and Device Locking
The Distributed Lock Manager (DLM) process coordinates access to
shared resources in the cluster. To do this, it provides the locking
mechanisms used to implement the necessary synchronization for
various filesystem operations. (Filesystem operations include, but are not
limited to, filesystem mounts, reads and writes of files, and the initial
creation of a filesystem.)
The operating system kernel uses the DLM to obtain the appropriate
lock(s) for all access and modification of files within a PSFS filesystem,
ensuring that all PSFS filesystem data are coherent across the cluster.
Similarly, the PSFS operations to create, mount, or check a filesystem are
mutually exclusive, and also use the DLM locking mechanisms.
The DLM provides the fundamental locking mechanisms to prevent
mutually exclusive operations from occurring at the same time within the
cluster, while allowing operations that can be performed concurrently to
proceed in parallel.