System information

Advanced Functions
5-9
4. You may also use multipath command to configure, list, and remove multi-path devices.
5. To add or remove LUNS, after completing the changes to the RAID system configurations, restart the service by
typing service multipathd restart. Modifying the configuration needs also to restart the service to make the
modifications effective.
6. If you’re running Linux cluster and need to have consistent multi-path device names, you need to use the alias option
in multipath.conf or to use the Linux persistent binding. For complete information, please go to RedHat and Novell
web site to find the following online documents:
- RedHat: “Using Device-Mapper Multipath”
- Novell SUSE: “SLES Storage Administration Guide”
5.1.6 MAC Multi-Path Solution
Mac OS X provides multi-path support on a basis since OS X 10.3.5, providing both path redundancy and load balancing.
Mac OS X implements miltipathing at the target device level, and it requires that the RAID controller presents the same
World Wide Node Name (WWNN) to all the host interfaces connected to the MAC systems. Please refer to •
Setting FC Worldwide Node Name on page 2-40 to select identical WWNN. After restarting the RAID system to make
this change effective, then follow 5.1.3 Configuring MPIO Hosts and RAID Controller on page 5-1 to complete the
LUN mapping configurations.
The Mac OS multipath I/O driver by default supports only round-robin I/O policy. With Apple Xsan software, you may set
the policy to be either round-robin (rotate) or static (failover-only). For more information please visit Apple web site and
read “Apple Xsan Administrator’s Guide”.
5.1.7 VMware ESX Server Multi-Path Solution
VMware ESX Server 2.5 or the later by default is loaded with hardware-independent multi-path drivers and management
interface. After completing the RAID system configurations and attaching the RAID system to the host computer, you may
use VMware Management Interface or the command, vmkmultipath or esxcfg-mpth, at Service Console to manage the
paths.
There are three multi-path policy options supported:
1. fixed -- using user-predefined path.
2. mru -- using most recently used path.
3. rr -- using round-robin algorithm, which is available only after ESX Server 3. The first two polices are use only one
active path, and move to a standby path only when the active path is down. The third policy can use all paths at the
same time to deliver the best performance. You may use esxcfg-advcfg to set path performance parameters. The
single-controller RAID system supports all the options.
When a cable is pulled, I/O freezes for approximately 30-60 seconds, until the SAN driver determines that the link is
down, and failover occurs. During that time, the virtual machines (with their virtual disks installed on a SAN) might appear
unresponsive, and any operations on the /vmfs directory might appear to hang. After the failover occurs, I/O should
resume normally.
After changing the configuration of LUN or paths, please use esxcfg-rescan command to do rescan and esxcfg-
vmhbadevs to know the mapping between device names and the LUNs.
For more information, please refer to VMware ESX Server Administration Guide and VMware ESX Server SAN
Configuration Guide, or go to http://www.vmware.com/.
5.1.8 Sun Solaris 10 OS Multi-Path Solution
The latest Sun Solaris OS 10 has integrated Storage Multipahting software, which offers path failover and a path
management utility. The single-controller RAID system is fully compliant with the software. After configuring the LUN
mappings and connecting the RAID system to Solaris system, you may find multi-path devices in the device directory with
their name of the following format: /dev/dsk/c3t2000002037CD9F72d0s0, which is largely different from non-multi-path
devices, /dev/dsk/c1t1d0s0.
The path management utility, mpathadm, allows you to list paths, list LUN discovered, configure auto-failover, and
control paths. Please check its man page. For more information about multi-path on Solaris, please refer to “Solaris Fibre
Channel and Storage Multipathing Administration Guide”, or go to Sun’s online document web site: http://docs.sun.com/
, and Sun’s online forum web: http://wikis.sun.com/.