3.5.1 Matrix Server Administration Guide

Chapter 7: Configure PSFS Filesystems 95

Filesystem Management and Integrity

Matrix Server uses the SANPulse daemon to manage PSFS filesystems.

SANPulse performs the following tasks:

• Coordinates filesystem mounts, unmounts, and crash recovery

operations.

• Checks for matrix partitioning, which can occur when matrix network

communications are lost but the affected servers can still access the

SAN. If this situation occurs, Matrix Server 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 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) daemon coordinates access to

shared resources in the matrix. 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 matrix.

Similarly, the PSFS operations to create, mount, or fsck 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

matrix, while allowing operations that can be performed concurrently to

proceed in parallel.