Administrator Guide

Device Mapper multipath for Linux
Topics:
• Overview
• Using Device Mapper Multipathing Devices (DMMP)
• Device Mapper configuration steps
• Linux host server reboot best practices
• Important information about special partitions
• Limitations and known issues
• Troubleshooting
Overview
The MD Series storage arrays use a Linux operating system software framework, known as Device Mapper (DM), to enable multipath
capabilities on Linux Host Servers. The DM multipath functionality is provided by a combination of physical disks and utilities. This chapter
describes how to use those utilities to complete the process of enabling MD Series storage arrays on a Linux system.
NOTE:
The required Device Mapper software components are installed on a Linux host server by running the MD Series
storage arrays resource DVD installation program on the server, and selecting either the Full or Host install option. For
detailed installation procedures, see the storage array’s Deployment Guide at Dell.com/support/manuals.
Benefits of using DM Multipath include:
• Detects path failure and re-routes I/O to other available paths
• Revalidates failed paths after path restoration
• Uses multiple available paths to maximize performance
• Reconfigures path usage based on path states and error conditions
• Unifies multiple device nodes into a single logical multipath device node
• Indentifies a new multipathed LU and automatically configures a new multipath node
• Provides device name persistency for Device Mapper (DM) devices under /dev/mapper/
Using Device Mapper Multipathing Devices
(DMMP)
NOTE:
Using or modifying any nodes other than the multipathing device nodes can result in array or file system
problems, including loss of communication with the array and corruption of the file system. Avoid accessing any device
other than the multipathing device.
NOTE: After creating a partition on a multipathing device, all I/O operations, including file system creation, raw I/O and
file system I/O, must be done through the partition node and not through the multipathing device nodes.
Prerequisites
The following tasks must be completed before proceeding. For more information about step 1 through step 3, see the storage array’s
Deployment Guide. For more information about step 4, see Creating Virtual Disks.
1. Install the host software from the MD Series storage arrays resource DVD — Insert the Resource media in the system to start the
installation of Modular Disk Storage Manager (MD Storage Manager) and Modular Disk Configuration Utility (MDCU).
NOTE: Installation of Red Hat 5.x requires a remount of the DVD media to make contents executable.
2. Reboot when prompted by the install program — The installation program prompts for and needs a reboot at completion of the
installation.
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