IBM Storwize V7000, Введение и руководство по внедрению

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IBM Flex System V7000 Storage Node Introduction and Implementation Guide
11.3.1 Session establishment and management
A
session
is the creation of a communication tunnel from the iSCSI initiator to the iSCSI
target. An iSCSI session consists of an
iSCSI login phase
and a
full feature phase
. At least
one session between the initiator and the target must be enabled through an iSCSI login
process. A login protocol data unit (PDU) is used to negotiate any variable parameters
between the two parties and can start a security routine to authenticate permissible
connectivity. When the login is successful, the target issues a login success to the initiator.
Otherwise, it issues an unsuccessful login. iSCSI can support multiple connections per
session (MCS) to increase aggregate bandwidth or, for several links, to improve reliability.
PDU structure
A
protocol data unit
is the basic message packet that travels between a client and target. It
consists of a basic header segment (BHS) and additional headers segments (AHS). It also
includes optional parameters, such as cyclic redundancy check (CRC) data segments and
data digests.
iSCSI error handling
An IP network is susceptible to the high probability of errors in data delivery. The iSCSI
protocol provides several measures to counter potential errors. The design requires iSCSI to
perform its functions within a Internet Protocol network safely and use appropriate quality of
service (QoS) procedures.
iSCSI security
The iSCSI can be used in networks where unauthorized data can be accessed, allowing for
different security methods. Encoding means, such as IPSec, which use lower levels, do not
require additional matching because they are transparent for higher levels, and for iSCSI.
Various solutions can be used for authentication, for example, CHAP, Kerberos, or private
keys exchange. An iSNS server can be used as a repository of keys.
11.3.2 iSCSI initiators
iSCSI initiators can be implemented by software or hardware. Software initiators can be
augmented by TCP-offload Ethernet adapters.
Software-only solutions
Software initiators and targets are virtual SCSI adapters that are written as part of the
operating environment. They use the processor resources and network adapters of the host
to transfer data. Software endpoints are easy to deploy and are low-cost or free with the host
operating system.
Software implementations can drive higher throughput than other implementations if sufficient
host processor resources are available. This higher throughput is especially true of cases
where smaller block sizes are used. Integration with the host operating system usually works
well, by using existing management tools and interfaces. Starting a host from an iSCSI device
is not possible when using software initiators unless a pre-startup execution environment
exists. At a minimum, a DHCP server and a file transfer protocol, such as Trivial File Transfer
Protocol (TFTP), are required.