Normally, DB engine needs cluster (2 nodes onwards) has to purchase extra SAN storage "partitions/domain" license for it. iSCSI is part of SAN storage. For SQL server clustering has to enable Windows "Enterprise" Server cluster license first before can go for it ( this is a practice if you honor the License agreement ). The SQL Server also needs "enterprise" license. It is good to get hardware principal/distributor to let you fill the "Sizing Questionnaire" in the proper spreadsheet & template since the proper sizing and LUN design is very important to enable DB cluster environment.