Red Hat GFS 6.0 -, Administrator'S Manual

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Chapter 8.
Using Clustering and Locking Systems
This chapter describes how to use the clustering and locking systems available with GFS, and consists
of the following sections:
•
Section 8.1 Locking System Overview
•
Section 8.2 LOCK_GULM
•
Section 8.3 LOCK_NOLOCK
8.1. Locking System Overview
The Red Hat GFS interchangeable locking/clustering mechanism is made possible by the
lock_harness.o
kernel module. The GFS kernel module
gfs.o
connects to one end of the
harness, and lock modules connect to the other end. When a GFS file system is created, the lock
protocol (or lock module) that it uses is specified. The kernel module for the specified lock protocol
must be loaded subsequently to mount the file system. The following lock protocols are available
with GFS:
•
LOCK_GULM — Implements both RLM and SLM and is the recommended choice
•
LOCK_NOLOCK — Provides no locking and allows GFS to be used as a local file system
8.2. LOCK_GULM
RLM and SLM are both implemented by the LOCK_GULM system.
LOCK_GULM is based on a central server daemon that manages lock and cluster state for all
GFS/LOCK_GULM file systems in the cluster. In the case of RLM, multiple servers can be run
redundantly on multiple nodes. If the master server fails, another "hot-standby" server takes over.
The LOCK_GULM server daemon is called
lock_gulmd
. The kernel module for GFS nodes using
LOCK_GULM is called
lock_gulm.o
. The lock protocol (LockProto) as specified when creating a
GFS/LOCK_GULM file system is called
lock_gulm
(lower case, with no
.o
extension).
Note
You can use the
lock_gulmd init.d
script included with GFS to automate starting
and stopping
lock_gulmd
. For more information about GFS
init.d
scripts, refer to
Chapter 12 Using GFS
init.d
Scripts .
8.2.1. Selection of LOCK_GULM Servers
The nodes selected to run the
lock_gulmd
server are specified in the
cluster.ccs
configuration file (
cluster.ccs:cluster/lock_gulm/servers
). Refer to
Section 6.5 Creating the
cluster.ccs
File .