Installation guide

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. T he 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 Section 2.1, “Linux Page Caching”.
Fencing GNBD server nodes, as described in Section 2.2, “Fencing GNBD Server Nodes”.
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 described in
Chapter 3, GNBD Driver and Command Usage.
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 Section 3.1, “Exporting a
GNBD from a Server” for more information about using the gnbd_export command for 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. T o physically remove a GNBD server node, you can use any fencing device: except the
following: fence_brocade fence agent, fence_vixel fence agent, fence_m cdata 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.
Chapter 2. Considerations for Using GNBD with Device-Mapper Multipath
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