It is not uncommon that hardware vendors have to fix their array controller firmware. In this case it is HP’s P2000 G3 firmware for the FC/iSCSI combined models. Again it is a fix for problems as a result of customers using bigger clusters. Here we have a problem with Windows Server 2008 R2 clusters which surfaces with bigger clusters, long IQN names and a maximum of the space available for SCSI-3 reservations. Haven’t we seen this kind of trouble before. I can assure you that admins of Hyper-V R2 clusters surpassing these limits weren’t all that happy.

Issue:
Using a long IQN name for iSCSI initiators may lead to issues while using SCSI-3 reservations and Persistent Group Reservations, particularly when trying to create large clusters with multiple paths to each LUN. A predefined area is used to store SCSI-3 reservation keys for each initiator path to each LUN and, when a large number of IQN entries are attempted to be stored, the array can run out of space in this area. This issue is dependent on the number of nodes and the number of paths per node accessing individual LUNs. This issue has been seen during the cluster validation process on Windows 2008 R2 clusters with 16 nodes, where each node had 4 paths to each LUN of the array.

Workaround:
Shorten the IQN name on the nodes.

The following formula is used to calculate the maximum IQN name length based on the number of cluster nodes and the number of paths from each node to a LUN on the array:

Maximum IQN Character Length = [3840 / (n * p)] – 16 (Where n = number of cluster nodes and p = number of paths per cluster node.)

NOTE: By specification, 223 is the maximum IQN length allowed.

The following table provides the calculated values based on the number of cluster nodes and the number of paths from each node to LUN on the array.

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Issue:
When using explicit LUN mapping, using long IQN names for the iSCSI Initiator can cause the array to map the LUN incorrectly. A predefined area is used to store explicit LUN mapping information per LUN and, with longer IQN names, this area can be exhausted. This issue is not dependent on the number of paths to the LUN.

Workaround:
Shorten the IQN name on the nodes.

The following formula is used to calculate the maximum IQN name length based on the number of hosts being explicitly mapped to a LUN on the array:

Maximum IQN Character Length = (4083 / n) – 7 (Where n = number of hosts nodes explicitly mapped to a LUN on the array.)

NOTE: By specification, 223 is the maximum IQN length allowed.

The following table provides the calculated values based on the number of hosts being explicitly mapped to a LUN on the array:

image

ftp://ftp.hp.com/pub/softlib2/software1/pubsw-linux/p296738768/v65347/631269-003_ReleaseNotes_TS201R015.htm