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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 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
-uor-Uwhen using thegnbd_exportcommand. 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.
