Creating MDisks on a system by using the CLI

You can use the command-line interface (CLI) to create MDisks on a system.

Attention: If you add an MDisk to a system as an MDisk, any data on the MDisk is lost. If you want to keep the data on an MDisk (for example, because you want to import storage that was previously not managed), you must create image mode volumes instead.

Assume that the system is set up and that a back-end controller is configured.

Ensure that all MDisks that are allocated to a single system are of the same RAID type. If the system has more than one tier of storage, ensure that all MDisks in the same tier are of the same RAID type. All of the MDisks in a system in the same tier must be similar and have similar performance characteristics. If not, the system must contain only one tier of storage, and all of the MDisks in the system must be similar and have similar performance characteristics.

Even with the best planning, circumstances can change and you must reconfigure your system after it is created. The data migration facilities that are provided by the controller enable you to move data without disrupting I/O.

Choosing a system's extent size

Consider the following factors as you plan the extent size of each new system:

You must specify the extent size when you create a new system.
You cannot change the extent size later; it must remain constant throughout the lifetime of the system.
Systems can have different extent sizes; however, this places restrictions on the use of data migration.
The extent size affects the maximum size of a volume in a system. A larger extent size increases the total amount of storage that the system can manage, and a smaller extent size allows more fine-grained control of storage allocation.

Important: You can specify different extent sizes for different systems; however, you cannot migrate (volumes) between systems with different extent sizes. If possible, create all your systems with the same extent size.

Issue the mkmdiskgrp CLI command to create a system.

Here is an example of the CLI command to create a system:

mkmdiskgrp -name maindiskgroup -ext 32 
 -mdisk mdsk0:mdsk1:mdsk2:mdsk3

maindiskgroup is the name of the system that you want to create, 32 MB is the size of the extent that you want to use, and mdsk0, mdsk1, mdsk2, mdsk3 are the names of the four MDisks that you want to add to the group.

You created and added MDisks to a system.

The following example provides a scenario where you want to create a system, but you do not have any MDisks available to add to the group. You plan to add the MDisks, later. You use the mkmdiskgrp CLI command to create the system bkpmdiskgroup and later used the addmdisk CLI command to add mdsk4, mdsk5, mdsk6, mdsk7 to the system.

Issue mkmdiskgrp -name bkpmdiskgroup -ext 32
bkpmdiskgroup is the name of the system that you want to create and 32 MB is the size of the extent that you want to use.
Find four MDisks that you want to add to the system.
Issue addmdisk -mdisk mdsk4:mdsk5:mdsk6:mdsk7 bkpdiskgroup
mdsk4, mdsk5, mdsk6, mdsk7 are the names of the MDisks that you want to add to the system and bkpdiskgroup is the name of the system for which you want to add MDisks.