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1.11. 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[1]
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[4]
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 1.2.1, “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
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 [5]
Note
It is possible to append a
--login option to a discovery command. This combines the two steps of discovering target portals and logging in to them. For example, iscsiadm --mode node --targetname proper_target_name --portal ip:port,target_portal_group_tag\ --login[5]
[4]
For information on how to retrieve a session's SID value, refer to Section 1.2.1, “iSCSI API”.
[5]
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.
