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CS C446 Data Storage Technologies & Networks. Agenda. Storage Area Networks Structure and Architecture Addressing Zoning, Trunking and Multipathing. Storage Area Networks. Storage units are on the network Network is (typically) different from the LAN Fibre-Channel SAN

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CS C446

Data Storage Technologies & Networks


Storage Area Networks

Structure and Architecture


Zoning, Trunking and Multipathing

Storage area networks
Storage Area Networks

  • Storage units are on the network

    • Network is (typically) different from the LAN

      • Fibre-Channel SAN

    • Data is accessed raw (in disk blocks) from storage units

      • As opposed to file access in NAS

  • Fibre-Channel SANs were the earliest:

    • FC offers high Bandwidth

  • Alternative SAN technologies available today:

    • E.g. IP SAN

  • SAN and NAS are converging:

    • E.g. NAS head with a SAN backend.

Sundar B.

San purpose
SAN - Purpose

  • Primary purpose

    • Aggregation of physical storage devices permitting logical, on-the-fly division/sharing among hosts

  • Non-functional requirements

    • High transfer rates

    • High availability

Sundar B.

San components and structure
SAN Components and Structure

  • Components

    • Hosts (client / server computers)

    • Storage Devices

    • Interfaces (ports for communication)

    • Hubs, Switches, and Gateways

  • Structure - Example

    • Storage devices thru’ ports are connected to an (FC) AL hub:

      • Local hosts are also connected to the AL via I/O bus adapters and ports

      • Hubs do not allow high transfer rate (due to sharing) but are cheap.

    • The hub is connected through a FC-switch to remote hosts (referred to as switched fabric)

      • Switches allow individual connections with high transfer rates but are expensive.

    • Gateways enable connection of SAN over WANs

      • SAN to SAN

      • SAN to hosts on the Internet

Sundar B.

San components and structure1
SAN Components and Structure

  • Interconnects

    • Cables – Fiber Optic Serial

    • Transceivers,

    • Interface Converters (Optical/Electrical),

    • Host-Bus Adapters (Parallel-Serial Conversion)

    • Inter Switch Links (connect E-ports)

  • Cascading

    • Seamless extension of fabric by adding switches

    • Interswitch links can also provide redundant paths

  • Devices

    • Hubs, Switched Hubs, Switches/Directors

    • Multiprotocol Routers (FCP, FCIP, iFCP, IP iSCSI)

Sundar B.

San addressing
SAN – Addressing

  • WWN

    • unique World Wide Name per N-port

    • Devices may have a WWN (independent of the adapters/ports)

    • Defined and maintained by IEEE

    • 64-bit long

    • 24-bit port addresses may be used locally to reduce overhead.

Sundar B.

San addressing1
SAN – Addressing

  • 24-bit addressing - in a switched fabric

    • Assigned by switch

    • At login, each WWN is assigned (mapped) to a 24-bit address by Simple Name Service (SNS)

      • SNS is a component of the fabric OS – acts as a registry/database

    • Address format:

      • domain address (bits 23-16) identifies the switch

        • Some addresses are reserved e.g broadcast;

        • 239 possible addrs.

      • area address (bits 15-8) identifies a group of F-ports,

      • port address (bits 7-0) identifies a specific N-port

    • Total addressible ports: 239x256x256

Sundar B.

San addressing2
SAN – Addressing

  • 24-bit addressing - in an AL

    • Obtained at loop initiation time and

    • re-assigned at login to the switch

    • Address Format:

      • Fabric loop address (bits 23-8) identifies the loop

        • All 0s denotes a private loop i.e., not connected to any fabric

      • Port address (bits 7-0) identifies a specific NL-port

        • Only 126 addresses are usable (for NL-ports):

        • 8B/10B encoding is used for signal balancing;

        • Out of the 256 bit patterns only 134 have neutral running disparity – 7 are reserved for FC protocol usage; 1 for an FL-port (so that the loop can be on the fabric);

Sundar B.

San routing
SAN – Routing

  • Routing

    • Analogous to switching in a LAN

    • Goal:

      • Keep a single path (bet. Any two ports) alive – no redundant paths or loops

      • Additional paths are held in reserve – may be used in case of failures.

    • Fabric Shortest Path First (FSPF) protocol –

      • Cost: hop count

      • Link state protocol

      • Link state database (or topology database) kept in switches

      • Updated/Initialized when switch is turned on or new ISL comes up or an ISL fails

    • Switches use additional logic when hop count is same.

      • Round Robin is often used for load sharing

Sundar B.

San zoning
SAN - Zoning

  • Zoning allows fabric segmentation:

    • Storage (traffic) isolation

      • E.g. Scenario: Windows systems claim all visible storage

    • Hardware Zoning: (1-1, 1-*, *-*)

      • Based on ports connected to fabric switches (switches-internal port numbering is used)

      • A port may belong to multiple zones

      • Adv: Implemented into a routing engine by filtering

      • Disadv: Device connections are tied to (physical) ports

    • Software Zoning:

      • Based on WWN – managed by the OS in the switch

      • Less secure due to spoofing possibilities

Sundar B.

San zoning1
SAN - Zoning

  • Software Zoning:

    • Based on WWN – managed by the OS in the switch

    • Number of members in a zone limited by memory available

    • A node may belong to more than one zone.

    • More than one sets of zones can be defined in a switch but only set is active at a time

      • Zone sets can be changed without bringing switch down

    • Less secure :

      • SZ is implemented using SNS

      • Device may connect directly to switch without going through SNS

      • WWN spoofing

      • WWN numbers can be probed

Sundar B.

San frame filtering
SAN – Frame Filtering

  • Frame Filtering

    • Process of inspecting each frame (header info.) at hardware level for access control purposes

    • Usually implemented as an ASIC w/ choice and configuration of filter that can be done at switch initialization/boot time.

      • Allows zoning to be implemented with access control performed at wire speed

      • Port level Zoning, WWN level Zoning, Device level Zoning, LUN level Zoning, and Protocol level Zoning can be implemented using Frame Filtering

Sundar B.

San trunking
SAN – Trunking

  • Trunking

    • Grouping of ISLs into a trunk i.e. a logical link

    • Useful for load sharing in the presence of zoning

      • i.e. zoning need not restrict ISL usage

    • Supports in-order end-to-end

      • Re-ordering done by the switch as required

Sundar B.

San multipathing
SAN – Multipathing

  • Multipathing

    • Provide multiple paths between a host and a device (LUN).

      • Redundancy for improved reliability and/or higher bandwidth for improved availability / performance

    • Channel subsystem of the kernel in switch OS handles multipathing at software level

      • Usually Separate device driver is used w/ following capabilities:

        • Enhanced Data Availability

        • Automatic path failover and recovery to alternative path

        • Dynamic Load balancing

        • Path selection policies

      • Failures handled:

        • Device Bus adapters, External SCSI cables, fibre connection cable, host interface adapters

      • Additional software needed for ensuring the host sees a single device.

Sundar B.

San lun masking
SAN - LUN Masking

  • Zoning imposes some logical traffic isolation as well as some access control of devices.

  • Alternative – LUN Masking:

    • Storage Device Control program (part of the switch OS) maintains an access lists for the storage device

      • One list per LUN

      • When hosts require access they request access to a LUN and the device control program verifies the list before granting access

Sundar B.

Storage virtualization
Storage Virtualization

  • Storage Virtualization

    • Integration of back-end devices and functions with front end functionality to provide certain abstractions.

  • Different levels:

    • Device Level

      • Physical devices are collected and presented as different virtual devices (e.g. partitions, RAID array controllers etc.)

    • File System Level

      • Block storage devices are presented as file systems

    • Fabric Level

      • Virtual Devices and collections are aggregated and presented as storage groups with high level access control (e.g. Zoning)

    • Server Level

      • Servers interpret the available storage as different units as per the requirement (Logical Volume Management at the host OS level)

Sundar B.

Storage virtualization1
Storage Virtualization

  • In-band implementation

    • Data and control flow thru’ same lines

    • Easy to implement

    • Homogeneous environment (even with heterogenous devices)

    • Scalable

  • Out-of-band implementation

    • Control flows through separate lines

    • Separate server(s) maintain metadata

      • Metadata: mapping tables, locking tables, access control

      • Server Known as metadata controller

    • Authentication needed for hosts

    • Add-on flexibility

      • E.g. Adding a file server / file system on a SAN environment

    • High Bandwidth availability for data traffic

Sundar B.

Emerging protocols
Emerging Protocols

  • iSCSI

  • iFCP

  • FCIP – FC tunnelling

Sundar B.