Creating LUNs, igroups, and LUN maps

Methods for creating LUNs, igroups, and LUN maps  

You use one of the following methods to create LUNs and igroups:

• Entering the lun setup command

  This method prompts you through the process of creating a LUN, creating an igroup, and mapping the LUN to the igroup. For information about this method, see Creating LUNs with the lun setup program.

• Using FilerView

  This method provides a LUN Wizard that steps you through the process of creating and mapping new LUNs. For information about this method, see Creating LUNs and igroups with FilerView.

• Entering a series of individual commands (such as lun create, igroup create, and lun map)

  Use this method to create one or more LUNs and igroups in any order. For information about this method, see Creating LUNs and igroups by using individual commands.

Note about using SnapDrive  

For Windows and some UNIX hosts, you can use SnapDrive for Windows or SnapDrive for UNIX to create and manage LUNs and igroups. If you use SnapDrive to create LUNs, you must use it for all LUN management functions. Do not use the Data ONTAP command line interface or FilerView to manage LUNs.

For information about the version of SnapDrive supported for your host environment, see the NetApp iSCSI S Support Matrix or NetApp FCP SAN Compatibility Matrix and the SnapDrive & SnapManager Compatibility Matrix at http://now.netapp.com/NOW/knowledge/docs/san/fcp_iscsi_config/
fcp_support.shtml.

Click the link for your host operating system. The compatibility matrix for your host lists the version of SnapDrive supported in a the section labeled "NetApp SnapDrive" or "Snapshot Integration".

What is required to create a LUN  

Whichever method you choose, you create a LUN by specifying the following attributes:

The path name of the LUN

The path name must be at the root level of a qtree or a volume in which the LUN is located. Do not create LUNs in the root volume. The default root volume is /vol/vol0.

For clustered storage system configurations, it is recommended that you distribute LUNs across the cluster.

Note
You might find it useful to provide a meaningful path name for the LUN. For example, you might choose a name that describes how the LUN is used, such as the name of the application, the type of data that it stores, or the user accessing the data. Examples are /vol/database/lun0, /vol/finance/lun1, or /vol/bill/lun2.

The host operating system type

The host operating system type (ostype) indicates the type of operating system running on the host that accesses the LUN, which also determines the following:

• Geometry used to access data on the LUN
• Minimum LUN sizes
• Layout of data for multiprotocol access

The LUN ostype values are solaris, windows, hpux, aix, linux, netware, vmware, and image. When you create a LUN, specify the ostype that corresponds to your host. If your host OS is not one of these values but it is listed as a supported OS in the appropriate support matrix, specify image.

For information about supported hosts, see the Fibre Channel Host Support Matrices or the iSCSI Solutions Support Matrices at http://now.netapp.com/NOW/knowledge/docs/san/fcp_iscsi_config/.

The size of the LUN

When you create a LUN, you specify its size as raw disk space, depending on the storage system and the host. You specify the size, in bytes (default), or by using the following multiplier suffixes.

The usable space in the LUN depends on host or application requirements for overhead. For example, partition tables and metadata on the host file system reduce the usable space for applications. In general, when you format and partition LUNs as a disk on a host, the actual usable space on the disk depends on the overhead required by the host.

The disk geometry used by the operating system determines the minimum and maximum size values of LUNs. For information about the maximum sizes for LUNs and disk geometry, see the vendor documentation for your host OS. If you are using third-party volume management software on your host, consult the vendor's documentation for more information about how disk geometry affects LUN size.

A brief description of the LUN (optional)

You use this attribute to store alphanumeric information about the LUN. You can edit this description at the command line or with FilerView.

A LUN identification number (LUN ID).

A LUN must have a unique LUN ID so the host can identify and access it. This is used to create the map between the LUN and the host. When you map a LUN to an igroup, you can specify a LUN ID. If you do not specify a LUN ID, Data ONTAP automatically assigns one.

Space reservation setting

When you create a LUN by using the lun setup command or FilerView, you specify whether you want to enable space reservation. When you create a LUN using the lun create command, space reservation is automatically turned on.

Note
It is recommended that you keep space reservation on.

About igroups  

Initiator groups (igroups) are tables of host identifiers (FCP WWPNs or iSCSI node names) that are used to control access to LUNs. Typically, you want all of the host's HBAs or software initiators to have access to a LUN. If you are using multipathing software or have clustered hosts, each HBA or software initiator of each clustered host needs redundant paths to the same LUN.

You can create igroups that specify which initiators have access to the LUNs either before or after you create LUNs, but you must create igroups before you can map a LUN to an igroup.

Initiator groups can have multiple initiators, and multiple igroups can have the same initiator. However, you cannot map a LUN to multiple igroups that have the same initiator.

Note
An initiator cannot be a member of igroups of differing ostypes. Also, a given igroup can be used for FCP or iSCSI, but not both.

FCP example

The following table illustrates how four igroups give access to the LUNs for four different hosts accessing the storage system. The clustered hosts (Host3 and Host4) are both members of the same igroup (aix-group2) and can access the LUNs mapped to this igroup. The igroup named aix-group3 contains the WWPNs of Host4 to store local information not intended to be seen by its partner.

iSCSI example

The following table shows two hosts and their igroups and LUNs.

Required information for creating an igroup  

Whichever method you choose, you create an igroup by specifying the following attributes:

The name of the igroup

This is a case-sensitive name that meets the following requirements:

• Contains 1 to 96 characters. Spaces are not allowed.
• Can contain the letters A through Z, a through z, numbers 0 through 9, hyphen ("-"), underscore ("_"), colon (":"), and period (".").
• Must start with a letter or number.

The name you assign to an igroup is independent of the name of the host that is used by the host operating system, host files, or Domain Name Service (DNS). If you name an igroup aix1, for example, it is not mapped to the actual IP host name (DNS name) of the host.

Note
You might find it useful to provide meaningful names for igroups, ones that describe the hosts that can access the LUNs mapped to them.

The type of igroup

The igroup type is either iSCSI (-i) or FCP (-f).

The ostype of the initiators

The ostype indicates the type of host operating system used by all of the initiators in the igroup. All initiators in an igroup must be of the same ostype. The ostypes of initiators are solaris, windows, hpux, aix, netware, vmware, and linux. If your host OS is not one of these values but it is listed as a supported OS in the appropriate support matrix, specify default.

iSCSI node names of iSCSI initiators

You can specify the node names of the initiators when you create an igroup. You can also add them or remove them later.

To know which node names are associated with a specific host, see the Host Support Kit documentation for your host. These documents describe commands that display the host's iSCSI node name.

WWPNs of the FCP initiators

You can specify the WWPNs of the initiators when you create an igroup. You can also add them or remove them later.

To know which WWPNs are associated with a specific host, see the Host Attach Kit documentation for your host. These documents describe commands supplied by the Attach Kit or the vendor of the initiator or methods that show the mapping between the host and its WWPN. For example, for Windows hosts, you use the lputilnt utility, and for UNIX hosts, you use the sanlun command. For information about using the sanlun command on UNIX hosts, see Creating an igroup using the sanlun command (UNIX hosts).

What is required to map a LUN to an igroup  

When you map the LUN to the igroup, you grant the initiators in the igroup access to the LUN. If you do not map a LUN, the LUN is not accessible to any hosts. Data ONTAP maintains a separate LUN map for each igroup to support a large number of hosts and to enforce access control.

You map a LUN to an igroup by specifying the following attributes:

LUN name

Specify the path name of the LUN to be mapped.

Initiator group

Specify the name of the igroup that contains the hosts that will access the LUN.

LUN ID

Assign a number for the LUN ID, or accept the default LUN ID. Typically, the default LUN ID begins with 0 and increments by 1 for each additional LUN as it is created. The host associates the LUN ID with the location and path name of the LUN. The range of valid LUN ID numbers depend on the host. For detailed information, see the documentation provided with your host attach kit.

Guidelines for mapping LUNs to igroups

Use the following guidelines when mapping LUNs to igroups:

• You can map two different LUNs with the same LUN ID to two different igroups without having a conflict, provided that the igroups do not share any initiators or only one of the LUNs is online at a given time.
• You can map a LUN only once to an igroup or a specific initiator.
• You can add a single initiator to multiple igroups. but the initiator can be mapped to a LUN only once. You cannot map a LUN to multiple igroups that contain the same initiator.
• You cannot use the same LUN ID for two LUNs mapped to the same igroup.

Making LUNs available on specific FCP target ports  

When you map a LUN to a Fibre Channel igroup, the LUN is available on all of the storage system's FCP target ports if the igroup is not bound to a portset. A portset consists of a group of FCP target ports. By binding a portset to an igroup, you make the LUN available on a subset of the system's target ports. Any host in the igroup can access the LUNs only by connecting to the target ports in the portset.

You define portsets for FCP target ports only. You do not use portsets for iSCSI target ports.

For detailed information about creating portsets and binding them to igroups, see Making LUNs available on specific FCP target ports.

Guidelines for LUN layout and space requirements  

When you create LUNs, use the following guidelines for layout and space requirements:

• Group LUNs according to their rate of change.

  If you plan to take Snapshot copies, do not create LUNs with high rate of change in the same volumes as LUNs with a low rate of change. When you calculate the size of your volume, the rate of change of data enables you determine the amount of space you need for Snapshot copies. Data ONTAP takes Snapshot copies at the volume level, and the rate of change of data in all LUNs affects the amount of space needed for Snapshot copies. If you calculate your volume size based on a low rate of change, and you then create LUNs with a high rate of change in that volume, you might not have enough space for Snapshot copies.

• Keep backup LUNs in separate volumes.

  It is recommended that you keep backup LUNs in separate volumes because the data in a backup LUN changes 100 percent for each backup period. For example, you might copy all the data in a LUN to a backup LUN and then move the backup LUN to tape each day. The data in the backup LUN changes 100 percent each day. If you want to keep backup LUNs in the same volume, calculate the size of the volume based on a high rate of change in your data.

• Quotas are another method you can use to allocate space. For example, you might want to assign volume space to various database administrators and allow them to create and manage their own LUNs. You can organize the volume into qtrees with quotas and enable the individual database administrators to manage the space they have been allocated.

  If you organize your LUNs in qtrees with quotas, make sure the quota limit can accommodate the sizes of the LUNs you want to create. Data ONTAP does not allow you to create a LUN in a qtree with a quota if the LUN size exceeds the quota.

Host-side procedures required  

The host detects LUNs as disk devices. When you create a new LUN and map it to an igroup, you must configure the host to detect the new LUNs. The procedure you use depends on your host operating system. On HP-UX hosts, for example, you use the ioscan command. For detailed procedures, see the documentation for your host support or attach kit.

Copyright © 1994-2005, Network Appliance, Inc. All rights reserved.
Part No. 210-01094_B0
File: c4cr-f11.htm
Last updated: 08-Dec-2005 13:25:25