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Chapter 11.
Using GNBD
GNBD (Global Network Block Device) provides block-level storage access over an Ethernet LAN.
GNBD components run as a client in a GFS node and as a server in a GNBD server node. A GNBD
server node exports block-level storage from its local storage (either directly attached storage or SAN
storage) to a GFS node.
This chapter describes how to use GNBD with Red Hat GFS and consists of the following sections:
•
Section 11.1 GNBD Driver and Command Usage
•
Section 11.2 Considerations for Using GNBD Multipath
•
Section 11.3 Running GFS on a GNBD Server Node
11.1. GNBD Driver and Command Usage
The Global Network Block Device (GNBD) driver allows a node to export its local storage as a GNBD
over a network so that other nodes on the network can share the storage. Client nodes importing the
GNBD use it like any other block device. Importing a GNBD on multiple clients forms a shared
storage configuration through which GFS can be used.
The GNBD driver is implemented through the following client and server kernel modules.
•
gnbd.o
— Implements the GNBD device driver on GNBD clients (nodes using GNBD devices).
• gnbd_serv.o
— Implements the GNBD server. It allows a node to export local storage over the
network.
Two user commands are available to configure GNBD:
• gnbd_export
(for servers) — User program for creating, exporting, and managing GNBDs on a
GNBD server.
• gnbd_import
(for clients) — User program for importing and managing GNBDs on a GNBD
client.
11.1.1. Exporting a GNBD from a Server
The
gnbd_serv.o
kernel module must be loaded on a node before it can export storage as a GNBD.
Once local storage has been identified to be exported, the
gnbd_export
command is used to export
it.
Caution
When configured for GNBD multipath, a GNBD server (a server that is exporting a GNBD) ignores
Linux page caching. Caching is ignored to ensure data integrity when using GNBD multipath. (By
default, the
gnbd_export
command exports with caching turned off.)