System information

Chapter 26. Device Mapper Multipathing and Virtual Storage
Red Hat Enterprise Linux 6 also supports DM-Multipath and virtual storage. Both features are
documented in detail in the Red Hat books DM Multipath and Virtualization Administration Guide.
26.1. Virt ual St orage
Red Hat Enterprise Linux 6 supports the following file systems/online storage methods for virtual
storage:
Fibre Channel
iSCSI
NFS
GFS2
Virtualization in Red Hat Enterprise Linux 6 uses l ibvi rt to manage virtual instances. The
l i bvi rt utility uses the concept of storage pools to manage storage for virtualized guests. A storage
pool is storage that can be divided up into smaller volumes or allocated directly to a guest. Volumes
of a storage pool can be allocated to virtualized guests. There are two categories of storage pools
available:
Lo cal st o rag e p o o ls
Local storage covers storage devices, files or directories directly attached to a host. Local
storage includes local directories, directly attached disks, and LVM Volume Groups.
Net wo rked ( sh ared ) st o rag e po o ls
Networked storage covers storage devices shared over a network using standard
protocols. It includes shared storage devices using Fibre Channel, iSCSI, NFS, GFS2, and
SCSI RDMA protocols, and is a requirement for migrating guest virtualized guests between
hosts.
Important
For comprehensive information on the deployment and configuration of virtual storage
instances in your environment, refer to the Virtualization Storage section of the Virtualization guide
provided by Red Hat.
26.2. DM-Mult ipat h
Device Mapper Multipathing (D M-Multipath) is a feature that 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.
DM-Multipath are used primarily for the following reasons:
Red u n d ancy
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
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