Red Hat GFS 6.0 -, Administrator'S Manual

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124 Chapter 11. Using GNBD
11.2.1. Linux Page Caching
For GNBD multipath, do not specify Linux page caching (the
-c
option of the
gnbd_export
com-
mand). All GNBDs that are part of the pool must run with caching disabled . Data corruption occurs if
the GNBDs are run with caching enabled. Refer to Section 11.1.1 Exporting a GNBD from a Server
for more information about using the
gnbd_export
command for GNBD multipath.
11.2.2. Lock Server Startup
Lock servers can reside on the following types of nodes: dedicated lock server nodes, GFS nodes,
or GNBD server nodes. In any case, a lock server must be running before the GNBD servers can be
started.
11.2.3. CCS File Location
In a GFS cluster configured for GNBD multipath, the location of CCS files for each node depends on
how a node is deployed. If a node is deployed as a dedicated GFS node, its CCS files can reside on a
GNBD, local storage, or FC-attached storage (if available). If a node is deployed as a dedicated GNBD
server, its CCS files must reside on local storage or FC-attached storage. If a node is deployed as a
dedicated lock server, its CCS files must reside on local storage or FC-attached storage. Because lock
servers need to start before GNBD servers can start, a lock server cannot access CCS files through a
GNBD. If a lock server is running on a GFS node, the CCS files for that node must be located on local
storage or FC-attached storage.
If a GNBD server that is exporting CCS files is also exporting GNBDs in multipath mode, it must
export the CCS files as read-only. (Refer to Section 11.1.1 Exporting a GNBD from a Server for more
information about exporting a GNBD as read-only.) Under those circumstances, a GNBD client cannot
use
ccs_tool
to update its copy of the CCS files. Instead, the CCS files must be updated on a node
where the CCS files are stored locally or on FC-attached storage.
Note
If FC-attached storage can be shared among nodes, the CCS files can be stored on that shared
storage.
Note
A node with CCS files stored on local storage or FC-attached storage can serve the CCS files to
other nodes in a GFS cluster via
ccs_servd
. However, doing so would introduce a single point of
failure. For information about
ccs_servd
, refer to Section 7.5.1 CCA File and Server .
Table 11-1 summarizes where CCS files can be located according to node deployment. For informa-
tion about using CCS, refer to Chapter 7 Using the Cluster Configuration System .