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Exploring Core AIX Performance-Monitoring Commands

More AIX commands systems programmers should know

Editor’s note: This article is the second in a two-part series. The first article can be found here on the IBM Systems Magazine, Power Systems — AIX edition Web site.

As you know, AIX has a vast array of commands that enable you to do a multitude of tasks. Depending on your needs, you use only a certain subset of these commands. These subsets differ from user to user and from need to need. However, there are a few core commands every user will commonly use.

In the first part of the series, I discussed commands that help you answer questions related to your OS hardware, version of AIX and kernels. In this article, I’ll outline information related to volume groups and logical volumes, networks, workload partitions and other performance monitoring tools. The intent is to provide a list you can use as a ready reference. While the behavior of these commands should be identical in all releases of AIX, they have been only tested in AIX 5.3.

Volume groups and logical volumes

How do I know if my volume group is normal, big, or scalable? Run the lsvg command on the volume group and look at the value for MAX PVs. The value is 32 for normal, 128 for big and 1,024 for scalable volume group.

How do I create a volume group? Use the following command, where s partition_size sets the number of megabytes (MB) in each physical partition where the partition_size is expressed in units of MB from one through 1,024. (It's one through 131,072 for AIX 5.3.)

mkvg -y name_of_volume_group -s partition_size list_of_hard_disks

The partition_size variable must be equal to a power of two (for example: one, two, four or eight). The default value for standard and big volume groups is the lowest value to remain within the limitation of 1,016 physical partitions per physical volume. The default value for scalable volume groups is the lowest value to accommodate 2,040 physical partitions per physical volume.

How can I change the characteristics of a volume group? You use the chvg command to change the characteristics of a volume group.

How do I create a logical volume? Type the following:

mklv -y name_of_logical_volume name_of_volume_group number_of_partition

How do I increase the size of a logical volume? To increase the size of the logical volume represented by the lv05 directory by three logical partitions, for example, type extendlv lv05 3.

How do I display all logical volumes that are part of a volume group (e,g, rootvg)? You can display all logical volumes that are part of rootvg by typing the following command: lsvg -l rootvg/

How do I list information about logical volumes? Run the following command to display information about the logical volume lv1: lslv lv1.

How do I remove a logical volume? You can remove the logical volume lv7 by running the following command: rmlv lv7. The rmlv command removes only the logical volume, but does not remove other entities, such as file systems or paging spaces that were using the logical volume.

How do I remove a copy of a logical volume? You can use the rmlvcopy command to remove copies of logical partitions of a logical volume. To reduce the number of copies of each logical partition belonging to logical volume testlv, ente: rmlvcopy testlv 2. Each logical partition in the logical volume now has at most two physical partitions.

Queries about volume groups: To show volume groups in the system, type lsvg. To show all the characteristics of rootvg, type lsvg rootvg. To show disks used by rootvg, type lsvg -p rootvg.

How to add a disk to a volume group? Type the following:

extendvg VolumeGroupName hdisk0 hdisk1 ... Hdiskn

How do I replace a disk?

1. extendvg VolumeGroupName hdisk_new
2. migratepv hdisk_bad hdisk_new
3. reducevg -d VolumeGroupName hdisk_bad

How do I mirror a logical volume?

1. mklvcopy LogicalVolumeName Numberofcopies
2. syncvg VolumeGroupName

How can I clone the rootvg? You can run the alt_disk_copy command to copy the current rootvg to an alternate disk. The following example shows how to clone the rootvg to hdisk1: alt_disk_copy -d hdisk1.

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