iSCSI is a licensed service on the filer that enables you to export LUNs and transfer block data to hosts using the SCSI protocol over TCP/IP.
In an iSCSI network, there are two types of nodes, targets and initiators. Targets are filers and initiators are hosts. Filers have storage devices, which are referred to as logical units of storage (LUNs,). Switches, routers, and ports are TCP/IP devices only and are not iSCSI nodes.
From the filer, a LUN is a logical representation of a physical unit of storage. It is a collection of, or a part of, physical or virtual disks configured as a single disk. When you create a LUN, it is automatically striped across many physical disks.
Data ONTAP manages LUNs at the block level, so it cannot interpret the file system or the data in a LUN.
From the host, LUNs appear as local disks on the host that you can format and manage to store data, using either the iSCSI or FCP protocols.
A LUN serial number is a unique 12-byte filer-generated ASCII string. Many multipathing software packages use this serial number to identify redundant paths to the same LUN. You can display the LUN serial number with the lun serial lun_path or the lun show -v command.
Filers and hosts can be connected directly to each other, or they can be connected to TCP/IP switches with Ethernet cable and use a TCP/IP network for all connectivity.
iSCSI is implemented over the target and initiator's standard Ethernet interfaces, unless you purchased an iSCSI Host Attach kit, which includes a vendor-provided HBA that is installed on the host. In that case, iSCSI is implemented through the HBA on the host.
On the filer, you can select which interface will be used for iSCSI traffic. For example, you can specify that iSCSI traffic will run exclusively over GbE interfaces and not the integrated 10/100 interface. Or you can specify that iSCSI traffic will run exclusively on an interface connected to a specific dedicated iSCSI network. You use the iswt interface command to control which network interface is used for iSCSI connectivity.
Note
If you want to use the internal 10/100 connection on the filer for management, NetApp strongly recommends that you set the Ethernet NIC, the host HBA, and the switch (if one is being used) to full duplex.
There are two ways you can configure a host to connect to an iSCSI network, depending on your host's operating system.
The filer does not use a hardware iSCSI HBA to implement the iSCSI service. The iSCSI protocol on the filer is implemented using a software driver that is integrated into Data ONTAP as a virtual adapter called the iSCSI Software Target (iswt). This virtual adapter is pre-installed on the filer. This provides two logical iswt adapters: iswta and iswtb. The iswta adapter controls all iSCSI traffic for the filer. If the filer is in a cluster, the iswtb adapter is dedicated to iSCSI traffic for the partner filer. If a failover occurs and the filer is operating in takeover mode, the iswtb adapter becomes active.
Every iSCSI node must have a node name. The two formats, or type designators, for iSCSI node names are iqn and eui. The target must use the iqn type designator. The initiator can use either the iqn or eui type designator.
This is a logical name. It is not linked to an IP address; rather, it is based on the following components:
The format is:
iqn.yyyy-mm.backward_naming_authority:unique_device_name
yyyy-mm is the month and year in which the naming authority acquired the domain name.
backward_naming_authority is the reverse domain name of the entity responsible for naming this device. An example reverse domain name is com.netapp.
unique_device_name is a free-format unique name for this device assigned by the naming authority.
The following example shows the iSCSI node name for an initiator that is an application server:
iqn.1987-06.com.initvendor1:123abc
Each filer has a default node name based on the NetApp reverse domain name and the serial number of the filer's NVRAM card in the following format:
iqn.1992-08.com.netapp:sn.serial_number.
The following example shows the default node name for a filer with the serial number 123456789:
iqn.1992-08.com.netapp:sn.123456789
The format is based on the following components:
The format is:
eui.nnnnnnnnnnnnnnnn
You can use the iscsi show initiator command or FilerView (click LUNs > Initiator Groups > Manage) to display the node names of the iSCSI initiators that are registered with the iSNS service, or that you set up manually.
You can use the iscsi nodename command to display the node name of the filer itself.
You can use the iscsi nodename command to change the filer node name. If you change the node name, it must be unique and it should be consistent.
iSCSI node names are used for the following purposes.
The host's node name is used to create initiator groups (igroups). An igroup is a collection of node names of initiators in an iSCSI network that you specify when you create the igroup. When you map a LUN on a filer to the igroup, you grant all the initiators in that group access to that LUN. If a host's node name is not in an igroup that is mapped to a LUN, that host does not have access to the LUN. This effectively masks access to the LUN.
The node name of the filer is used to uniquely identify each iswt target port on a filer.
The Internet Storage Name Service (iSNS) is a protocol that enables automated discovery and management of iSCSI devices on an TCP/IP storage network. An iSNS server maintains information about active iSCSI devices on the network, including their IP addresses, iSCSI node names, an portal groups.
If you have an iSNS server on your network, and it is configured and enabled for use by both the initiator and the filer, the filer will automatically register its IP address, node name, and portal groups with the iSNS server when the iSNS service is started. The iSCSI initiator can query the iSNS server to discover the filer as a target device.
If you do not have an iSNS server on your network, you must manually configure each target to be visible to the host. For information on how to do this, see the appropriate iSCSI host initiator Support Kit or the iSCSI Host Bus Adapter Attach Kit documentation for your specific host.
The Challenge Handshake Authentication Protocol (CHAP) enables authenticated communication between iSCSI initiators and targets. When you use CHAP authentication, you define CHAP user names and passwords on both the initiator and the filer.
During the initial stage of an iSCSI session, the initiator sends a login request to the filer to begin the session. The login request includes the initiator's CHAP user name and algorithm. The filer responds with a CHAP challenge. The initiator provides a CHAP response. The filer verifies the response and authenticates the initiator. The CHAP password is used to compute the response.
During an iSCSI session, the initiator and the target communicate over their standard Ethernet interfaces, unless the host has a vendor-supplied HBA. The filer appears as a single iSCSI target node with one iSCSI node name. The filer supports one TCP connection per iSCSI session.
An iSCSI session can be conducted over a filer virtual network interface (vif) or a virtual LAN (VLAN) interface.
The iSCSI software adapter maps each Ethernet interface on the target to a single portal group. In this way, an initiator port can conduct simultaneous iSCSI sessions on the target, with one session for each portal group. The iswt driver allows 1024 simultaneous sessions, depending on the memory capacity of the filer. To determine whether your host's initiator software can take advantage of this functionality, see your host documentation.
Each session has an Initiator Session ID (ISID), a number that is determined by the initiator.
The following options are automatically enabled when the iSCSI service is turned on.
You can use the NetApp Cluster Configuration Checker to detect inconsistent settings on clusters licensed for iSCSI.
To download and run the Cluster Configuration Checker, log in to the NOW Web site at http://now.netapp.com and go to Software Downloads > Tools & Utilities.
If you purchased a MultiStoreTM licence and created vFilerTM virtual filers, you can enable the iscsi license for each vFiler to manage LUNs and igroups on a per vFiler basis. For information about vFilers, see Creating LUNs on vFilers and the sections on iSCSI service on vFilers or LUNs on vFilers in the MultiStore Management Guide.
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Part No. 210-00571
File: c1ov-i3.htm
Last updated: 11/21/03 17:01:26