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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 un-
available, 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 consid-
eration:
•
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
described in
Chapter 3, GNBD Driver and Command
1. Linux Page Caching
For GNBD with device-mapper multipath, do not specify Linux page caching (the
the
command). All GNBDs that are part of a logical volume must run with caching
gnbd_export
disabled. Data corruption occurs if the GNBDs are run with caching enabled. Refer to
"Exporting a GNBD from a Server"
for GNBD with device-mapper multipath.
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
agent,
fence agent,
fence_sanbox2
BD fencing device (
fence_gnbd
about configuring fencing for GNBD server nodes, refer to the Global File System manual.
Section 1, "Linux Page
or
when using the
-U
gnbd_export
for more information about using the
fence agent,
fence_scsi
fence agent) to fence a GNBD server node. For information
Caching".
Section 2, "Fencing GNBD Server
command. Exporting GNBD devices is
Usage.
fence agent,
fence_vixel
fence agent. In addition, you cannot use the GN-
2
Nodes".
option of
-c
Section 1,
command
gnbd_export
fence
fence_mcdata
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