RHEL 6 Storage Admin - 21.12. Scanning iSCSI Interconnects

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21.12. Scanning iSCSI Interconnects

For iSCSI, if the targets send an iSCSI async event indicating new storage is added, then the scan is done automatically. Cisco MDS™ and EMC Celerra™ support this feature.

However, if the targets do not send an iSCSI async event, you need to manually scan them using the iscsiadm utility. Before doing so, however, you need to first retrieve the proper --targetname and the --portal values. If your device model supports only a single logical unit and portal per target, use iscsiadm to issue a sendtargets command to the host, as in:

iscsiadm -m discovery -t sendtargets -p target_IP:port^[7]

The output will appear in the following format:

target_IP:port,target_portal_group_tag proper_target_name

For example, on a target with a proper_target_name of iqn.1992-08.com.netapp:sn.33615311 and a target_IP:port of 10.15.85.19:3260, the output may appear as:

10.15.84.19:3260,2 iqn.1992-08.com.netapp:sn.33615311
10.15.85.19:3260,3 iqn.1992-08.com.netapp:sn.33615311

In this example, the target has two portals, each using target_ip:ports of 10.15.84.19:3260 and 10.15.85.19:3260.

To see which iface configuration will be used for each session, add the -P 1 option. This option will print also session information in tree format, as in:

    Target: proper_target_name
        Portal: target_IP:port,target_portal_group_tag
           Iface Name: iface_name

For example, with iscsiadm -m discovery -t sendtargets -p 10.15.85.19:3260 -P 1, the output may appear as:

Target: iqn.1992-08.com.netapp:sn.33615311
    Portal: 10.15.84.19:3260,2
       Iface Name: iface2
    Portal: 10.15.85.19:3260,3
       Iface Name: iface2

This means that the target iqn.1992-08.com.netapp:sn.33615311 will use iface2 as its iface configuration.

With some device models (e.g. from EMC and Netapp), however, a single target may have multiple logical units and/or portals. In this case, issue a sendtargets command to the host first to find new portals on the target. Then, rescan the existing sessions using:

iscsiadm -m session --rescan

You can also rescan a specific session by specifying the session's SID value, as in:

iscsiadm -m session -r SID --rescan^[10]

If your device supports multiple targets, you will need to issue a sendtargets command to the hosts to find new portals for each target. Then, rescan existing sessions to discover new logical units on existing sessions (i.e. using the --rescan option).

Important

The sendtargets command used to retrieve --targetname and --portal values overwrites the contents of the /var/lib/iscsi/nodes database. This database will then be repopulated using the settings in /etc/iscsi/iscsid.conf. However, this will not occur if a session is currently logged in and in use.

To safely add new targets/portals or delete old ones, use the -o new or -o delete options, respectively. For example, to add new targets/portals without overwriting /var/lib/iscsi/nodes, use the following command:

iscsiadm -m discovery -t st -p target_IP -o new

To delete /var/lib/iscsi/nodes entries that the target did not display during discovery, use:

iscsiadm -m discovery -t st -p target_IP -o delete

You can also perform both tasks simultaneously, as in:

iscsiadm -m discovery -t st -p target_IP -o delete -o new

The sendtargets command will yield the following output:

ip:port,target_portal_group_tag proper_target_name

For example, given a device with a single target, logical unit, and portal, with equallogic-iscsi1 as your target_name, the output should appear similar to the following:

10.16.41.155:3260,0 iqn.2001-05.com.equallogic:6-8a0900-ac3fe0101-63aff113e344a4a2-dl585-03-1

Note that proper_target_name and ip:port,target_portal_group_tag are identical to the values of the same name in Section 21.2.1, “iSCSI API”.

At this point, you now have the proper --targetname and --portal values needed to manually scan for iSCSI devices. To do so, run the following command:

iscsiadm --mode node --targetname proper_target_name --portal ip:port,target_portal_group_tag \ --login ^[11]

Using our previous example (where proper_target_name is equallogic-iscsi1), the full command would be:

iscsiadm --mode node --targetname \ iqn.2001-05.com.equallogic:6-8a0900-ac3fe0101-63aff113e344a4a2-dl585-03-1 \ --portal 10.16.41.155:3260,0 --login^[11]

^[10] For information on how to retrieve a session's SID value, refer to Section 21.2.1, “iSCSI API”.

^[11] This is a single command split into multiple lines, to accommodate printed and PDF versions of this document. All concatenated lines — preceded by the backslash (\) — should be treated as one command, sans backslashes.