Red Hat GNBD WITH GLOBAL FILE SYSTEM IN RHEL 4.5 Instalační příručka stáhnout pdf (Strana 9)

Chapter 1.

Device Mapper Multipathing

Device Mapper Multipathing (DM-Multipath) allows you to configure multiple I/O paths between server

nodes and storage arrays into a single device. These I/O paths are physical SAN connections that can

include separate cables, switches, and controllers. Multipathing aggregates the I/O paths, creating a

new device that consists of the aggregated paths.

1.1. New and Changed Features for Red Hat Enterprise

Linux 5.7

Red Hat Enterprise Linux 5.7 includes the following documentation and feature updates and changes.

• The new configuration file parameters fast_io_fail_tmo, dev_loss_tmo, and file_timeout

are documented in Chapter 4, The DM-Multipath Configuration File.

• The procedure for ensuring that multipath devices names are consistent across the nodes in a

cluster has been expanded in Section 2.2, “Consistent Multipath Device Names in a Cluster”.

1.2. Overview of DM-Multipath

DM-Multipath can be used to provide:

• Redundancy

DM-Multipath can provide failover in an active/passive configuration. In an active/passive

configuration, only half the paths are used at any time for I/O. If any element of an I/O path (the

cable, switch, or controller) fails, DM-Multipath switches to an alternate path.

• Improved Performance

DM-Multipath can be configured in active/active mode, where I/O is spread over the paths in a

round-robin fashion. In some configurations, DM-Multipath can detect loading on the I/O paths and

dynamically re-balance the load.

Figure 1.1, “Active/Passive Multipath Configuration with One RAID Device” shows an active/passive

configuration with two I/O paths from the server to a RAID device. There are 2 HBAs on the server, 2

SAN switches, and 2 RAID controllers.

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Red Hat GNBD WITH GLOBAL FILE SYSTEM IN RHEL 4.5 Instalační příručka Strana 9