Quite a few people want to use IET with Oracle, here is the information regarding disk caching and reservation from Ozgur from Oracle.
The SCSI2 and SCSI3 reservation features are not required by Oracle RAC with Oracle clusterware. SCSI3 PR is a requirement of “Veritas” clusterware. So any iSCSI implementation without PR would be ok with Oracle RAC and clusterware. RAC/PCW needs the following:
1. No buffering anywhere in the chain between the Oracle write and the disk subsystem This is provided via raw devices, OCFS or ASM.
2. Persistent naming of devices (by any means): The devices are needed to be named consistently for use of the Oracle clusterware (PCW).
So as long as you use default write-through mode in IET, disable all write cache in disk drive with hdparm, and use ScsiId or ScsiSN parameter for your LU, you are ready to go!