Target ISID Problems

We have recently found a large number of the targets in the market space are incorrectly handling the iSCSI ISID. The ISID is the initiator part of the session identifier. An I_T_Nexus between an iSCSI initiator and target is created by the combination of the following parts.

iSCSI Initiator Name + ',i,'+ ISID, iSCSI Target Name + ',t,'+ Portal Group Tag (iSCSI RFC Section 2.1)

The problem we are seeing with many targets is they are ignoring the ISID in this I_T_Nexus. When a second session is connecting to the target with the same initiator-name and a different ISID some targets are treating this second session the same as the first. This means the first session is implicitly disconnected and the second session is treated as the first reconnecting (Connection Reinstatement iSCSI RFC Section 5.3.4).

Users with these misbehaving targets can encounter this problem with the Microsoft iSCSI initiator or with Solaris 10 Update 2 initiator (Solaris Express 12/05). As part of Solaris 10 Update 2 we have added some new abilities for multipathing that will allow the creation of multiple Sessions to the same iSCSI Target Name/Portal Group Tag. I will present more details on this feature in the future.

In the mean time I recommend target vendors correct this problem with one of two approaches.

• If your array doesn't have the resources to handle more that one session from a specific initiator-name. Then on login if the ISID is different than the original ISID return the following login failure. Status Class == 0x03 and Status Detail == 0x02, "Target has incufficient session, connection, or other resources."
• The other option is to properly record and support the ISID field so multiple sessions for the same initiator-name are supported.

Fixing this issue now will help your customers avoid problems in the future. If your an array vendor and have more questions on this problem email them to iscsi-support-ext at sun dot com.

Posted at 08:12AM Nov 22, 2005 by dweibel in General  |  Comments[0]