6.5.1

Discovery
A discovery session is part of the iSCSI protocol. It returns the set of targets you can access on an iSCSI
storage system. The two types of discovery available on ESXi are dynamic and static. Dynamic discovery
obtains a list of accessible targets from the iSCSI storage system. Static discovery can access only a
particular target by target name and address.
For more information, see Configuring Discovery Addresses for iSCSI Adapters.
Authentication
iSCSI storage systems authenticate an initiator by a name and key pair. ESXi supports the CHAP
authentication protocol. To use CHAP authentication, the ESXi host and the iSCSI storage system must
have CHAP enabled and have common credentials.
For information on enabling CHAP, see Configuring CHAP Parameters for iSCSI Adapters.
Access Control
Access control is a policy set up on the iSCSI storage system. Most implementations support one or more
of three types of access control:
n
By initiator name
n
By IP address
n
By the CHAP protocol
Only initiators that meet all rules can access the iSCSI volume.
Using only CHAP for access control can slow down rescans because the ESXi host can discover all
targets, but then fails at the authentication step. iSCSI rescans work faster if the host discovers only the
targets it can authenticate.
Error Correction
To protect the integrity of iSCSI headers and data, the iSCSI protocol defines error correction methods
known as header digests and data digests.
Both parameters are disabled by default, but you can enable them. These digests pertain to, respectively,
the header and SCSI data being transferred between iSCSI initiators and targets, in both directions.
Header and data digests check the noncryptographic data integrity beyond the integrity checks that other
networking layers provide, such as TCP and Ethernet. They check the entire communication path,
including all elements that can change the network-level traffic, such as routers, switches, and proxies.
The existence and type of the digests are negotiated when an iSCSI connection is established. When the
initiator and target agree on a digest configuration, this digest must be used for all traffic between them.
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