vsphere-esxi-vcenter-server-55-storage-guide

Using ESXi with iSCSI SAN 10You can use ESXi in conjunction with a storage area network (SAN), a specialized high-speed network thatconnects computer systems to high-performance storage subsystems. Using ESXi together with a SANprovides storage consolidation, improves reliability, and helps with disaster recovery.To use ESXi effectively with a SAN, you must have a working knowledge of ESXi systems and SANconcepts. Also, when you set up ESXi hosts to use Internet SCSI (iSCSI) SAN storage systems, you must beaware of certain special considerations that exist.This chapter includes the following topics:• “iSCSI SAN Concepts,” on page 69• “How Virtual Machines Access Data on an iSCSI SAN,” on page 74iSCSI SAN ConceptsIf you are an administrator who plans to set up ESXi hosts to work with iSCSI SANs, you must have aworking knowledge of iSCSI concepts.iSCSI SANs use Ethernet connections between computer systems, or host servers, and high performancestorage subsystems. The SAN components include iSCSI host bus adapters (HBAs) or Network InterfaceCards (NICs) in the host servers, switches and routers that transport the storage traffic, cables, storageprocessors (SPs), and storage disk systems.iSCSI SAN uses a client-server architecture. The client, called iSCSI initiator, operates on your host. Itinitiates iSCSI sessions by issuing SCSI commands and transmitting them, encapsulated into iSCSI protocol,to a server. The server is known as an iSCSI target. The iSCSI target represents a physical storage system onthe network. It can also be provided by a virtual iSCSI SAN, for example, an iSCSI target emulator runningin a virtual machine. The iSCSI target responds to the initiator's commands by transmitting required iSCSIdata.iSCSI MultipathingWhen transferring data between the host server and storage, the SAN uses a technique known asmultipathing. Multipathing allows you to have more than one physical path from the ESXi host to a LUN ona storage system.Generally, a single path from a host to a LUN consists of an iSCSI adapter or NIC, switch ports, connectingcables, and the storage controller port. If any component of the path fails, the host selects another availablepath for I/O. The process of detecting a failed path and switching to another is called path failover.For more information on multipathing, see Chapter 23, “Understanding Multipathing and Failover,” onpage 215.VMware, Inc. 69