3 Setting Up LSM

This chapter describes how to set up the Logical Storage Manager (LSM). It describes how to reenable LSM after an installation, as well as how to set up LSM for the first time.

To begin using LSM, you must initialize disks or partitions for LSM use and configure the disks into an LSM disk group. Figure 3-1 is a conceptual representation showing how disks are placed under LSM control.

Figure 3-1: Configuring Disks into an LSM Disk Group

3.1 Preparing for Digital UNIX Installation

If you are already running LSM, perform the following steps before performing a full installation of Digital UNIX:

Make a backup copy of the /etc/vol/volboot file. You will need to restore this file after the full installation.
If LSM volumes are in use for the root (/), swap, /usr, or /var file systems, unencapsulate the LSM volumes. Refer to Section C.20 and Section C.19 for unencapsulation instructions and examples.
You will need to reencapsulate the file systems and swap devices after the installation of Digital UNIX.
Use the /usr/sbin/volsave command to save the current copy of the LSM configuration. Copy the saved LSM configuration to tape. Refer to Section 7.4 and Section C.21 for details.

See the Installation Guide for complete information on preinstallation tasks for LSM.

3.2 Reenabling LSM after a Reinstallation

If you are already running LSM and the rootdg disk group is already initialized, you do not need to reenable LSM. For example, if you have already performed an upgrade installation, skip this section.

If you had LSM initialized on a system before doing a full installation, you can reenable the LSM configuration by performing the following steps:

Copy the /etc/volboot file from a backup:
# cp /backup/volboot /etc/volboot
Create the LSM special device file:
# /sbin/volinstall
Start the LSM daemons and volumes:
# /sbin/vol-startup

3.3 Initializing LSM

If you are setting up LSM for the first time, you can use either of the following approaches to initialize and configure disks for use with LSM.

Use the volsetup utility to create the LSM configuration database for the first time. Then, use the voldiskadd utility to add more disks into LSM. This is the simplest method to set up an LSM configuration.
Use a series of LSM low-level commands (for example, voldisksetup, voldg, voldctl) to create the database for the first time and later add new disks into an existing LSM configuration. Although this method is more complicated, it allows more control over your LSM configuration and environment.

These two approaches are described in the following sections. See also Appendix C for detailed examples of setup procedures.

3.3.1 Using the volsetup Utility

The volsetup utility provides an easy way to initialize LSM. This utility automatically modifies disk labels, initializes disks for LSM, creates the default disk group, rootdg, and configures disks into the rootdg disk group. Note that you invoke the volsetup utility only once. To later add more disks, use the voldiskadd utility (as described in Section 6.2.1).

The volsetup utility prompts you to estimate how many disks will be managed by LSM. The utility uses the estimate to define optimal values for the private region size (in sectors), and the number of configuration and log copies per disk. The default values for LSM configurations are shown in Table 3-1.

Table 3-1: Default Values for LSM Configurations

Number of Disks	Private Region Size	nconfig and nlog
1 to 4	1024	2
5 to 8	1024	1
More than 8	1024	1 for first 8 disks, 0 for others
More than 128	1536	1 for first 8 disks, 0 for others
More than 256	2048	1 for first 8 disks, 0 for others

Follow these steps to use volsetup:

If you are in single-user mode, set the host name for your system before initializing LSM.
Execute the /sbin/volsetup interactive utility by entering the following command:
# /sbin/volsetup rz1

In this example, the disk rz1 is used to initialize the rootdg disk group. If you do not give the name of a disk, LSM prompts you. Refer to the volsetup(8) reference page for information on how to handle partition overlap error messages.
Note
When you are first setting up LSM, do not include the boot disk in the disks you specify to volsetup. After you have initialized LSM, you can encapsulate the root and swap partitions and add them to the rootdg disk group. See Section 5.2 for details.
The volsetup utility modifies the /etc/inittab file. On a system reboot, LSM is started automatically by the LSM entries in the inittab file. (See inittab(4) for more information.)
The LSM script /sbin/lsmbstartup starts the LSM daemon vold and the error daemon voliod. After running the volsetup procedure, check that the vold daemon is running. See Section 14.4 for more information.

The volsetup utility creates the /etc/vol/volboot file. This file is used to locate copies of the rootdg disk group configuration when the system starts up. Do not delete the /etc/vol/volboot file; it is critical for starting LSM. To update the volboot file, use voldctl; do not manually edit /etc/vol/volboot.

3.3.2 Initializing LSM with Individual Commands

As an alternative to using the volsetup command (described in Section 3.3), you can use individual LSM commands to initialize and configure disks for use with LSM. Use individual LSM commands when you need additional flexibility and control to match the LSM configuration to a site's particular needs and to optimize performance. You use individual LSM commands to perform the following tasks:

Modify the disk's label and set up a private region on the disk.
Add the disk into an LSM disk group.
Add the disk to the /etc/vol/volboot file.

The following sections describe how to use LSM commands to accomplish these tasks.

3.3.2.1 Initializing /etc/vol/volboot, Starting vold, and Initializing the rootdg Disk Group

Follow these steps to initialize /etc/vol/volboot, start the vold daemon and initialize the rootdg disk group:

If you are in single-user mode, set the host name for your system, as follows:
# /sbin/hostname hostname
Create a special device file using the following command:
# /sbin/volinstall
Start vold in the disabled mode using the following command:
# /sbin/vold -m disable
Initialize /etc/vol/volboot using the following command:
# voldctl init
Initialize the rootdg disk group using the following command:
# voldg init rootdg

Note
You can use the voldg init command only once to create a disk group.

3.3.2.2 Selecting Private Region Parameters

Use the LSM individual commands described here to create and initialize the private region on the disk:

Set the number of configuration databases and the number of log regions with the nconfig and nlog options, respectively, using the guidelines described in Table 3-2. Starting with LSM Version 4.0, the default value for these options is 1.

Whenever a disk group contains a large number of disks, distribute the disks that contain a configuration database and kernel change log across different controllers. By distributing the data across multiple controllers, you obtain higher availability.

Table 3-2: Settings for nconfig and nlog

If you expect to have...	Then...
Up to four disks in the disk group	Set the `nconfig` and `nlog` options to 2.
Up to eight disks in the disk group	Use the default value of 1 for the `nconfig` and `nlog` options.
More than eight disks in the disk group	Initialize the first eight disks by setting the `nconfig` and `nlog` options to 1, and initialize the remaining disks by setting the `nconfig` and `nlog` options to 0.

Set the size of the private region with the privlen option using the guidelines described in Table 3-3.

Table 3-3: Private Region Sizes

If you plan to add the disk to...	Then...
An existing disk group	Set the private region size for the disk large enough to accommodate the disk group's current database size.
A new disk group that does not currently exist (but you plan to create the new diskgroup)	Try to estimate the future growth of the disk group and include additional space as you determine the disk's private region size.

Note
Adding a disk with a smaller private region size than what is in use by other disks in a disk group can shrink the diskgroup's configuration database size.

Typically, the private region size should be a minimum of 512 sectors and a maximum of 2048 sectors. Starting with LSM Version 4.0, the default private region size is 1024 sectors. For systems configured with 128 or fewer physical disks, you can use the default private region size. With this value, the private region's configuration database can usually contain up to 1400 records, which is sufficient for systems configured with as many as 128 disks (assuming a typical configuration that has approximately 8 records per disk).

Determine the number of records needed in an LSM configuration database. To do this consider the following:
- Each object (volume, plex, subdisk, and disk) created in the disk group requires one record in the configuration database.
- The size of each LSM record varies. Approximately two records can fit in one sector (512 bytes).
- Disks that will be added to the rootdg disk group need one record for each LSM disk group.
- Disks that will be added to the rootdg disk group need one record for each disk in all other disk groups.
- Certain LSM configuration changes (for example, moving a subdisk) involve creating and later deleting two to four temporary records to perform the operation.
- Forecast expected disk growth and allow additional records to handle that growth.
- Private regions that contain two configuration database copies will cut in half the number of records available.

The following sections show how to initialize and add disks to an LSM environment.

3.3.2.3 Initialize Disk Label and Add to LSM

Use the voldisksetup utility to initialize a disk for LSM use. The disk must already have a disk label.

The utility modifies the disk's label and initializes the private region. The private region contains:

The disk header
The table of contents
Zero or more copies of the configuration database
Zero or more copies of the kernel change log

The voldisksetup utility performs actions that are equivalent to using the disklabel and voldisk commands.

The following examples of the voldisksetup command demonstrate how to initialize a complete disk and how to initialize a disk partition ( rz8 and rz10d) for use with LSM:

# voldisksetup -i rz8 nconfig=1 privlen=1024

# voldisksetup -i rz10d nconfig=1 privlen=1024

See the voldisksetup(8) reference page for more information about the voldisksetup command, its options, and partition overlap error messages.

Note
To add a disk with no configuration database, set the nconfig attribute to 0 when initializing the disk with voldisksetup. Do not initialize a new disk as a nopriv disk - this disk type is appropriate only for encapsulation of existing data.

3.3.2.4 Adding a Disk to a Disk Group

To create a new disk group, use the voldg init command, as show in Section 3.3.2.1. After the disk group is created, you can add other disks into the disk group using the voldg adddisk command. For example, the following command line shows how to add another disk to the rootdg disk group:

# voldg -g rootdg adddisk disk02=rz10d

See the voldg(8) reference page for more information about this command and its options.

3.3.2.5 Disks Added to /etc/vol/volboot

When LSM is initialized, the disks in rootdg are added to the /etc/vol/volboot file.

When the system is booted, LSM uses information contained in the /etc/vol/volboot file to find the location of at least one disk that was added to the rootdg disk group. Using the configuration database on the disk listed in /etc/vol/volboot, LSM obtains information about the LSM disks, disk groups, and other configuration data necessary to start up LSM.

3.3.2.6 Starting LSM Manually

To manually start LSM, take the following actions:

Start two error daemons by entering the following:
# voliod set 2
Start up vold in enabled mode by entering the following:
# vold -k

If vold is running in disabled mode, enter the following:
# voldctl enable
Enable the LSM volumes by entering the following:
# volrecover -sb

3.4 Increasing the Configuration Limits

When you configure LSM, the default limit set for the number of volumes and plexes allowed per system is smaller than the maximum number allowed. The default and maximum LSM limits are shown in Table 3-4.

Table 3-4: Configuration Limits

LSM Object	Default Limit per System	Maximum Limit per System
Volumes[Table Note 1]	1021	4093
Plexes	1024	4096
Subdisks per plex	4096	4096

Table note:

These limits include the reserved volumes rootvol and swapvol. Three additional volume minor numbers are reserved for future use.

You can increase the default number of volumes allowed on a system by editing the /etc/sysconfigtab file. For example, to increase the maximum number of volumes allowed on the system from 1024 to 2048 volumes, edit the /etc/sysconfigtab file and add the following lines:

lsm:
       max-vol=2048

The change to /etc/sysconfigtab will take affect on the next system reboot. Note that in this example lsm is the name of the subsystem and max-vol is the attribute that is being changed. The maximum number of plexes allowed per system is the same as the maximum number of volumes configured on the system. If the attribute max-vol is not specified in /etc/sysconfigtab, LSM uses its default.

To boot the system with a different value for max-vol than either the default number of volumes or the value of max-vol specified in /etc/sysconfigtab, boot the system in interactive mode. For example, the value of max-vol can be set to 3072 by specifying maxvol=3072 when the system is booted interactively, as shown here:

>>> boot -fl i
............... ............... ............... [Enter kernel name ... ] vmunix maxvol=3072

In this example, the value 3072 overrides the value of max-vol that is set in the /etc/sysconfigtab file and the default value of 1024.

See the sysconfigtab(4) reference page for information on the format used for the /etc/sysconfigtab file.

3.5 Post-Setup Tasks

After you have initialized LSM, there are several other steps you should complete to begin using LSM:

Encapsulate existing LVM volumes, UFS file systems, and AdvFS file systems that you want to put under LSM control. See Chapter 4.
Encapsulate and mirror the root and swap partitions. See Chapter 5.
Create new LSM volumes. See Chapter 7.
Use the volsave command to save copies of your configuration files. See Section 7.4 for information on using this command.