In some cases, it is possible to run into limitations or bugs within a particular ISCSI implementation that may require you to tune your ISCSI settings for storage initiators on each of your Oracle VM Servers.
Typically this is required when you experience an IO lock on a LUN and an unexpected change in the kernel workload on the Oracle VM Server. You may also notice a dramatic increase in network traffic between the Oracle VM Server and the storage array. This particular case has been noted to occur on some ZFS appliances running Oracle Solaris 11 and is related to the Sun iSCSI COMSTAR port provider. The problem can usually be resolved by updating package versions, however if this is not an option you may tune your ISCSI settings on each Oracle VM Server that communicates with a SUN.COMSTAR target to enable flow control.
To tune ISCSI, on each Oracle VM Server, perform the following steps:
Open
/etc/iscsi/iscsid.confin a text editor.Locate the section titled
iSCSI settings.Change the value of the entry
node.session.iscsi.InitialR2Ttoyes, and the value of the entrynode.session.iscsi.ImmediateDatatono.Save the file.
Restart the ISCSI daemon by issuing the following command:
# service iscsid restart
The preferred resolution to this issue is to update your software. Manual configuration of Oracle VM Server settings is not generally advisable, as changes may be lost during future updates.