Transcript Introduction to iSCSI - UNH-IoL

UNH InterOperability Lab
iSCSI
Introduction
Improving Networks Worldwide.
iSCSI
Contents
• Definition of iSCSI
• iSCSI vs Fibre Channel
• iSCSI Session Types
• Key Negotiation Overview
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iSCSI
Definition of iSCSI
• iSCSI is a Storage Area Network (SAN)
protocol that allows for SCSI command
transmission over a TCP/IP network
• iSCSI allows for the sharing of I/O
devices over a long distance, especially
storage devices
– Typically high speed disk arrays
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iSCSI
Definition of iSCSI Continued
• iSCSI maintains the SCSI notion of an
Initiator and Target device
• iSCSI removes the traditional bus
structure of SCSI and maps SCSI over a
network
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iSCSI
Bus vs Network Architecture
Bus Architecture
Network Architecture
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iSCSI
Problems Mapping SCSI to a Network
• In order not to violate Bus model of SCSI,
there can only ever be one (1) concurrent
Session between an iSCSI Initiator and iSCSI
Target
– Commonly called “The ISID Rule”
• Multiple Connections may exist within that
Session, but all Connections must contain the
same Initiator Session Identifier (ISID)
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iSCSI
iSCSI vs Fibre Channel
• Both protocols have advantages and
disadvantages
– iSCSI is typically less expensive
– Fibre Channel is typically faster
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iSCSI
iSCSI
• iSCSI is traditionally less expensive
than Fibre Channel to implement
– Can be done with only software
• iSCSI can run over preexisting copper
infrastructure and use preexisting
switches and routers
• iSCSI does not require specially trained
network administrators to manage the
network
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iSCSI
Fibre Channel
• In most cases, Fibre Channel will outperform
iSCSI in data transfer speeds
• Fibre Channel requires a special fiber
network to be created in order to be
implemented
• Total Cost of Ownership (TCO) is much
higher than iSCSI
– Special network, administrators, fiber
maintenance, etc.
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iSCSI
Comparison Conclusion
• Fiber Channel is much faster than traditional
iSCSI
– iSCSI Extensions for RDMA (iSER) aims to
lessen this difference
• iSCSI can run over preexisting copper
infrastructure
– iSCSI devices can be accessed over the
Internet
• In almost all cases, iSCSI is less expensive to
implement and maintain
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iSCSI
iSCSI Session Types
• iSCSI has two (2) Session types
– Discovery
– Normal
• Each Session has two (2) Phases
– Login
– Contains Security Negotiation and Operational
Parameter Negotiation
– Full Feature Phase
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iSCSI
Discovery Session
• A Discovery Session is used to allow
the iSCSI Initiator to find iSCSI Targets
that it can connect to
• The Initiator must explicitly tell the
Target that the Session to be created be
a Discovery Session
– SessionType=Discovery
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iSCSI
Login within Discovery
• Allows the
Initiator and
Target to
establish 'who' it
is
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iSCSI
Full Feature Phase within Discovery
• Once the Login Phase has completed, the Session
can transfer into Full Feature Phase (FFP)
• Within a Discovery Session, FFP allows the
sending of Text Requests (Initiator) and Text
Responses (Target)
– Used to let the Target inform the Initiator what
devices it can access
• No other types of data units may be transmitted
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iSCSI
Discovery Session
• Initiator transmits
the SendTargets
key to the Target
• Target replies
with a list of
devices accessible
to the Initiator
and their
addresses
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iSCSI
Discovery Session
• Once a Discovery Session has
completed, the Session must be
terminated
• If the Initiator then desires to perform
data I/O, a Normal Session must be
created
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iSCSI
Normal Session
• An iSCSI Initiator will explicitly tell the
iSCSI Target that the Session to be
created is a Normal Session
• A Normal Session is defined in RFC
3720 to be an unrestricted session
• Access to SCSI devices can only be
achieved while in a Normal Session
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iSCSI
Login within Normal Session
• Allows the Initiator and Target to
declare/negotiate data transmission
rules and other connection settings
– Ex. Size of individual data units, number of
simultaneous data transfers
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iSCSI
Full Feature Phase in Normal Session
• Once Full Feature
Phase (FFP)
within a Normal
Session has been
reached, data I/O
can take place
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iSCSI
Key Negotiation Overview
• All iSCSI parameters are contained
within key=value pairs
– Ex. “TargetAlias=UNH-IOL”
• Some keys are declared and others are
negotiated
– Declared keys do not need a response from
the receiver
– Negotiated keys must always receive a
response from the receiver
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iSCSI
iSCSI Key Negotiation
• Key negotiations can
allow the enabling or
disabling of features
• Also allows for value
negotiation or
declaration
• Ex. MaxBurstLength=512
More on Key Negotiation will be
covered in the iSCSI Login
Presentation
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iSCSI
Summary
• iSCSI is a low cost, low maintenance
alternative to Fibre Channel
• iSCSI networks can use existing copper
infrastructures
• Unlike Fibre Channel, iSCSI networks
can span the Internet
• iSCSI Key Negotiation allows for
enabling/disabling of features as well
as value negotiations
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