vSphere Storage - ESXi 5.1 - Documentation - VMware

Using ESXi with iSCSI SAN 10
You can use ESXi in conjunction with a storage area network (SAN), a specialized high-speed network that
connects computer systems to high-performance storage subsystems. Using ESXi together with a SAN provides
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 SAN concepts.
Also, when you set up ESXi hosts to use Internet SCSI (iSCSI) SAN storage systems, you must be aware of
certain special considerations that exist.
This chapter includes the following topics:
n “iSCSI SAN Concepts,” on page 71
n “How Virtual Machines Access Data on an iSCSI SAN,” on page 76
iSCSI SAN Concepts
If you are an administrator who plans to set up ESXi hosts to work with iSCSI SANs, you must have a working
knowledge of iSCSI concepts.
iSCSI SANs use Ethernet connections between computer systems, or host servers, and high performance
storage subsystems. The SAN components include iSCSI host bus adapters (HBAs) or Network Interface Cards
(NICs) in the host servers, switches and routers that transport the storage traffic, cables, storage processors
(SPs), and storage disk systems.
iSCSI SAN uses a client-server architecture. The client, called iSCSI initiator, operates on your host. It initiates
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 on the network.
It can also be provided by a virtual iSCSI SAN, for example, an iSCSI target emulator running in a virtual
machine. The iSCSI target responds to the initiator's commands by transmitting required iSCSI data.
iSCSI Multipathing
When transferring data between the host server and storage, the SAN uses a technique known as multipathing.
Multipathing allows you to have more than one physical path from the ESXi host to a LUN on a storage system.
Generally, a single path from a host to a LUN consists of an iSCSI adapter or NIC, switch ports, connecting
cables, and the storage controller port. If any component of the path fails, the host selects another available
path 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 20, “Understanding Multipathing and Failover,” on
page 193.
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