VERITAS Volume Manager 3.5 Administrator's Guide (September 2002)

Disabling and Enabling Multipathing for Specific Devices

88 VERITAS Volume Manager Administrator’s Guide

Load Balancing

DMP uses the balanced path mechanism to provide load balancing across paths for

active/active disk arrays. Load balancing maximizes I/O throughput by using the total

bandwidth of all available paths. Sequential I/O starting within a certain range is sent

down the same path in order tobeneﬁt from disk track caching. Large sequential I/O that

does not fall within the range is distributed across the available paths to reduce the

overhead on any one path.

For active/passive disk arrays, I/O is sent down the primary path. If the primary path

fails, I/O is switched over to the other available primary paths or secondary paths. As the

continuous transferof ownership of LUNs fromone controller toanother results insevere

I/O slowdown, load balancing across paths is not performed for active/passive disk

arrays.

Note Both paths of an active/passive array are not considered to be on different

controllerswhen mirroring across controllers (forexample, whencreating a volume

using vxassist make speciﬁed with the mirror=ctlr attribute).

Disabling and Enabling Multipathing for Speciﬁc Devices

You can use vxdiskadm menu options17 and18 to disable or enable multipathing. These

menu options also allow you to exclude devices from or include devices in the view of

VxVM. For more information, see “Disabling Multipathing and Making Devices Invisible

to VxVM,” and “Enabling Multipathing and Making Devices Visible to VxVM” on

page 93.

Disabling Multipathing and Making Devices Invisible to VxVM

Note Some of the operations described in this section require a reboot of the system.

Select menu task 17 (Prevent multipathing/Suppress devices from VxVM’s

view) from the vxdiskadm main menu to prevent a device from being multipathed by

the VxVM DMP driver (vxdmp), or to exclude a device from the view of VxVM:

1. At the following prompt, conﬁrm that you want to continue:

Exclude Devices

Menu: VolumeManager/Disk/ExcludeDevices

This operation might lead to some devices being suppressed from

VxVM’s view or prevent them from being multipathed by vxdmp (This

operation can be reversed using the vxdiskadm command).