Considerations For Using Gnbd With Device-Mapper Multipath; Linux; Fencing Gnbd Server Nodes - Red Hat ENTERPRISE LINUX 4 - GLOBLAL NETWORK BLOCK DEVICE Using Instructions

Chapter 2.
Considerations for Using GNBD with
Device-Mapper Multipath
GNBD with device-mapper multipath allows you to configure multiple GNBD server nodes (nodes
that export GNBDs to GFS nodes) to provide redundant paths to the storage devices. The GNBD
server nodes, in turn, present multiple storage paths to GFS nodes via redundant GNBDs. When using
GNBD with device-mapper multipath, if a GNBD server node becomes unavailable, another GNBD
server node can provide GFS nodes with access to storage devices.
If you are using GNBD with device-mapper multipath, you need to take the following into
consideration:
• Linux page caching, as desribed in
• Fencing GNBD server nodes, as described in
• GNBD device names; export names for GNBD devices must be unique. Additionally, you must
specify the -u or -U when using the gnbd_export command. Exporting GNBD devices is
Chapter 3, GNBD Driver and Command
described in
2.1. Linux Page Caching
For GNBD with device-mapper multipath, do not specify Linux page caching (the -c option of
the gnbd_export command). All GNBDs that are part of a logical volume must run with caching
disabled. Data corruption occurs if the GNBDs are run with caching enabled. Refer to
"Exporting a GNBD from a Server"
GNBD with device-mapper multipath.

2.2. Fencing GNBD Server Nodes

GNBD server nodes must be fenced using a fencing method that physically removes the nodes from
the network. To physically remove a GNBD server node, you can use any fencing device: except the
following: fence_brocade fence agent, fence_vixel fence agent, fence_mcdata fence agent,
fence_sanbox2 fence agent, fence_scsi fence agent. In addition, you cannot use the GNBD
fencing device (fence_gnbd fence agent) to fence a GNBD server node. For information about
configuring fencing for GNBD server nodes, refer to the Global File System manual.
Section 2.1, "Linux Page
Section 2.2, "Fencing GNBD Server
Usage.
for more information about using the gnbd_export command for
Caching".
Nodes".
Section 3.1,
3