Change Logical Drive Ownership/Preferred Path; Edit Topology - Add Free Capacity Started - IBM DS3000 Introduction And Implementation Manual

Draft Document for Review August 30, 2007 12:59 am
Figure 10-19 Edit Topology - Add Free Capacity Started

10.3.4 Change Logical Drive Ownership/Preferred Path

If you are using a dual controller version of the DS3000, each logical drive has a preferred
controller of ownership. This controller normally handles all I/O requests for this particular
logical drive. In other words, each logical drive is owned by one and only one controller at any
point in time. The alternate controller only takes over and handles the I/O requests if there is a
failure in the I/O path, for example, a defective HBA or switch.
When defining logical drives, the system normally alternates ownership between the two
controllers - workload is not taken into account. Therefore, you could end up with a
configuration where there is an imbalance - so that one controller is handling much more I/O
than the other. To balance the workload between the controllers, you can change the
preferred ownership of a logical drive to the other controller. To change the preferred
ownership of a logical drive, the controller path itself must be active - you cannot change the
ownership of a drive if it is temporarily being handled by its alternate controller.
Important: Be sure that the operating system using the logical drive uses a multipath I/O
driver. Otherwise, it loses access to the logical drive.
Balancing traffic is unfortunately not always a trivial task. For example, if an application
requires large disk space to be located and accessed in one chunk, it becomes harder to
balance traffic by spreading the smaller volumes among controllers.
In addition, typically, the load across controllers and logical drives is constantly changing. The
logical drives and data accessed at any given time depend on which applications and users
are active during that time period, hence the importance of monitoring the system.
The preferred controller ownership of a logical drive or array is the controller of an
active-active pair that is designated to own these logical drives. The preferred controller
owner is the controller that currently owns the logical drive or array.
If the preferred controller is undergoing a firmware download, ownership of the logical drives
is automatically shifted to the other controller, and that controller becomes the current owner
of the logical drives. If the preferred controller need to be replaced, you should disable the
controller first. This will intentionally cause a failover of LUNs to the other controller and allow
the preferred controller to be removed and replaced. This is considered a routine ownership
change and is reported with an informational entry in the event log.
7065Admin_Modify.fm
Chapter 10. Administration - Modify
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