iSCSI Requirements draft-haagens-ips-iscsireqs-00.txt Randy Haagens - - PowerPoint PPT Presentation

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iSCSI Requirements draft-haagens-ips-iscsireqs-00.txt Randy Haagens - - PowerPoint PPT Presentation

Jan 05, 2024 586 likes •754 views

iSCSI Requirements draft-haagens-ips-iscsireqs-00.txt Randy Haagens Director, Networked Storage Architecture Hewlett-Packard Co. Randy_Haagens@ hp.com 05 J ul 2000 P age 1 Applicability (Scope) iSCSI is a mapping of SCSI-3 to TCP, a

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SLIDE 1

P age 1 05 J ul 2000

iSCSI Requirements

draft-haagens-ips-iscsireqs-00.txt Randy Haagens Director, Networked Storage Architecture Hewlett-Packard Co. Randy_Haagens@ hp.com

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SLIDE 2

August 10, 2000 P age 2 R andy Haagens

Applicability (Scope)

  • iSCSI is a mapping of SCSI-3 to TCP, a “SCSI transport”
  • Volume/ Block storage on IP Networks (L

AN, MAN and W AN)

  • Analogous to today’s SAN architectures

– Typically using Ethernet instead of Fibre Channel

  • Using SCSI protocol

– SCSI for volume/ block storage (NFS and CIFS for file storage)

  • Gateways to other SCSI interconnects

– Fibre Channel, Parallel-bus, potentially others

  • Benefit from IP/ Ethernet infrastructure
  • Increasing performance and reduced cost
  • Seamless conversion from local to wide area using IP routers
  • Emerging availability of “IP datatone” services
  • Protocols and middleware for management, security and Q oS
  • Economics arising from a single type of network
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SLIDE 3

August 10, 2000 P age 3 R andy Haagens

Applicability (Scope)

  • Applications
  • L
  • cal storage access, consolidation and pooling
  • Remote disk access (as for a storage utility)
  • L
  • cal and remote synch and asynch mirroring between controllers
  • L
  • cal and remote backup and restore
  • Evolution with SCSI to support emerging object storage model
  • Topologies
  • Point-to-point direct connection
  • Dedicated storage L

AN, consisting of one or more L AN segments

  • Shared L

AN, carrying a mix of traditional L AN plus storage traffic

  • L

AN-to-W AN extension using IP routers or carrier “IP datatone”

  • Private networks and the public Internet
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SLIDE 4

August 10, 2000 P age 4 R andy Haagens

iSCSI Solution Topology

Gigabit Ethernet H

hba nic

FC SAN H

hba

Gigabit Ethernet FC SAN H

hba

WAN IP Datatone FC Port controller

(gateway) GbE Switch dvr SCSI-TCP WAN Service Campus Extension Wide area extension Host computer with EtherSAN Host computer with FC Native storage array TCP connections What’s new

HBA and driver Native array

attachment

Protocol controller FC Switch

FC array

Controller Controller

JBOD

Controller

JBOD

Controller

JBOD

Controller

JBOD

Tape

Native tape

attachment

Controller

Tape

SCSI Port

controller (gateway) Other SCSI peripherals

Controller

JBOD

FC array

Controller

JBOD

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SLIDE 5

August 10, 2000 P age 5 R andy Haagens

Management “Appliance” HP-NT

iSCSI Solution Topology

Remote console PC(s)

...

Site Network

Router

Storage Network Centralized Mgmt Storage Management (only)

Router

Storage Data (only) Corporate WAN Storage WAN Servers

...

The two WANs may be combined, at some risk to security and QoS Storage networks are isolated between cells

Controller

JBOD

Filer

JBOD

Controller

Tape

Stor Serv

Con

JB

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SLIDE 6

27 J ul 2000 P age 6 R andy Haagens

4.12 The SCSI model for distributed communications

SCSI Protocol Services Physical Interconnect Services SCSI Application L ayer SCSI Protocol L ayer a.k.a. SCSI Transport

[SAM-2 § 1.2]

Physical Interconnect L ayer SCSI Protocol Services Physical Interconnect Services Protocol Service Interface Physical Interconnect Service Interface SAM and Command Standards [26] SPC-2, SBC-2, &c. SCSI Protocol Standard [26] SIP, FCP-2, SBP-2, SST, SVP, SSA- S3P/ SSA-TL 2, iSCSI/ TCP/ IP Physical Interconnect Standard [26] SPI, SPI-2, FC-PH-3, FC-FS/ PI, FC-AL , IEEE1394, SSA-PH-2, 802.2/ 802.3 Initiator I/ O System Client Target I/ O System Server Server R equest →

←Server R

esponse [5] Service Delivery Subsystem

Composite of SAM -2 Fig.s 2, 5, 6, 7, 9, 26, 28

Service Delivery Port Service Delivery Port

Application Client L

  • gical Unit

Device Server Task Manager Device Service R equest →

←Device Service R

esponse [6] Task Management R equest →

←Task M anagement R

esponse [6]

SCSI Device SCSI Device SCSI Application SCSI Application SCSI Application Protocol [26] SCSI Protocol [26] Physical Interconnect [26]

P rocedure definitions here [SAM -2 §5,6,7]

P rotocol Service R equest →

←P

rotocol Service Confirmation P rotocol Service R esponse →

←P

rotocol Service Indication

SAM -2

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SLIDE 7

05 J ul 2000 iSCSI Architecture P age 7 R andy Haagens

SCSI Multiport Target Unit

Domain Device Service Delivery Subsystem Service Delivery Port Interconnect Subsystem Target Target Identifier (64b) SM U Domain Device Service Delivery Subsystem Service Delivery Port Interconnect Subsystem Target Task M anager L

  • gical Unit

(L U) L

  • gical Unit

(L U) Target Identifier (64b)

§4.7.4; §6 §4.8

L U N umber (L UN ) (64b) Device Server Task Set Task Set Untagged Task Untagged Task Tagged Task Tagged Task

O ne or more L UN s §7 O ne or more task sets per L UN . O ne per “initiator” Starts from 0. N ot a W W N . May be remapped. See §4.10.1 and SPC-2 §8.4.4 for a discussion of Device Identifiers a.k.a. SCSI Device Identifier or Device Identifier §4.7.2

Device Identification page (83h) “L UN W W N ”

SPC-2 §8.4.3

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SLIDE 8

August 10, 2000 P age 8 R andy Haagens

SCSI-layer Issues

  • Naming of SCSI targets and L

Us

  • 64b Target ID limitation imposed by SAM-2
  • Names vs. addresses of SCSI L

Us

  • 3rd party copy (reference to L

U)

  • Compatibility with new Access Controls model [T10/ 99-245 rev 8]
  • Multi-port device model
  • W hat exactly is a SCSI Service Delivery Port in the iSCSI session

model?

  • In-order delivery of Task requests (commands)
  • SCSI attributes that control ordering of task execution depend on in-
  • rder task delivery
  • iSCSI layer is complicated by need to deliver tasks in order

– Command numbering

  • Gateway architecture
  • Gateways to parallel SCSI and SCSI-FCP are contemplated
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SLIDE 9

27 J ul 2000 iSCSI Architecture P age 9 R andy Haagens

iSCSI Multiport Target Unit

Domain Device Target Target Target ID (128B) SM U Task M anager L

  • gical Unit

(L U) L

  • gical Unit

(L U)

§4.7.4; §6 §4.8

L U N umber (L UN ) (64b) Device Server Task Set Task Set Untagged Task Untagged Task Tagged Task Tagged Task

§7 O ne or more task sets per L UN . O ne per “initiator” Starts from 0. N ot a W W N . May be remapped See §4.10.1 and SPC-2 §8.4.4 for a discussion of Device Identifiers a.k.a. SCSI Device Identifier or Device Identifier §4.7.2

Device Identification page (83h) “L U W W N ”

SPC-2 §8.4.3 Extend to accommodate url

L UN M ap Service Delivery Port(s) Service Delivery Port(s) TCP Connection(s) TCP Connection(s) Service Delivery Subsystem Interconnect Subsystem iSCSI Session(s) iSCSI Session(s) Domain Device Target Target Target ID (128B) L UN M aps L UN M aps Service Delivery Port(s) Service Delivery Port(s) Service Delivery Subsystem Interconnect Subsystem iSCSI Session(s) iSCSI Session(s) Access ID Access ID IP Addr(s) IP Addr(s) TCP Connection(s) TCP Connection(s) IP Addr(s) IP Addr(s) Access ID Access ID

Domains are isolated networks L UN Map used generally is a function of the Service Delivery P

  • rt, Target ID and the Access

ID. P referred implementation makes the L UN map a function only of the Target ID; not all targets may be reachable from a given Service Delivery P

  • rt; Access ID

authorizes access to a given Target. preferred permitted L ist of Access IDs is an ACL Multiple target “views”

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SLIDE 10

August 10, 2000 P age 10 R andy Haagens

iSCSI-layer Issues

  • Naming
  • URL

syntax proposed: scsi:/ / <domain-name>[/ modifier]

  • Include SCSI “target” in name? Views, mapping
  • URL

syntax: length problem (SCSI Target ID 64b limit)

  • Connection allegiance
  • SCSI task command/ data/ status in same TCP connection
  • Session Concept
  • A group of TCP connections
  • Supports ordered command striping for bandwidth aggregation
  • Recovery from TCP connection failure

– SCSI task retry – “Replay buffer” may be required

  • Possibly need an iSCSI layer CRC
  • Concern about TCP’s checksum robustness
  • More end-to-end even than TCP
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SLIDE 11

05 J ul 2000 P age 11 R andy Haagens

SAM-2 Service Delivery Port

FC-2 Framing FC-1 Coding (FC-FS) Physical TCP IP 802.2 LLC / Ethernet Framing FC-0 Physical Interface (FC-PI) iSCSI FC-3 Common Services FC-4 SCSI-FCP 802.3 Media Access

SAM-2, SCSI-3 Commands

SCSI Protocol Services Physical Interconnect Services Initiator I/ O System Client Service Delivery Port

Application Client

SCSI Device SCSI Application

P rotocol Service R equest →

←P

rotocol Service Confirmation

PHY TCP IP LLC iSCSI MAC TCP TCP

W ith channel bonding / port aggregation 3.1.89 service delivery port: service delivery port: service delivery port: service delivery port: A device-resident interface used by the application client, device server or task manager to enter and retrieve requests and responses from the service delivery subsystem. Synonymous with “port” (3.1.61) 4.6 …the Service Delivery Port object represents the hardware and software that implements the protocols and interfaces between servers or clients in the SCSI Device and the Interconnect Subsystem. 3.1.81 SCSI M ulti-port unit: SCSI M ulti-port unit: SCSI M ulti-port unit: SCSI M ulti-port unit: A device that has multiple service delivery ports (see 3.1.89) or responds to multiple SCSI device identifiers (see 3.1.79)...

iSCSI iSCSI iSCSI PHY IP LLC MAC PHY IP LLC MAC

Protocol Service Interface

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SLIDE 12

August 10, 2000 P age 12 R andy Haagens

iSCSI Session Concept

TCP iSCSI iSCSI iSCSI iSCSI PHY IP LLC MAC TCP PHY IP LLC MAC TCP PHY IP LLC MAC SCSI TCP iSCSI iSCSI iSCSI iSCSI PHY IP LLC MAC TCP PHY IP LLC MAC TCP PHY IP LLC MAC SCSI

TCP provides N reliable byte streams through the network fabric Some per-stream processing can be done by an iSCSI module (message formatting). N o communication among stacks is assumed. R estrict iSCSI session layer processing to be needed only upon transmission of SCSI command and receipt of SCSI status.

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SLIDE 13

August 10, 2000 P age 13 R andy Haagens

TCP-layer Issues

  • Recovery of data stream processing following segment drop
  • Segment drop may result in loss of iSCSI framing

– Unable to move data to final location until framing is recovered – Pipe may contain 250 MB of data (at 10 Gbps)

  • RDMA or a framing mechanism may solve the problem
  • Error detection
  • L

ink layer is not end-to-end in IP networks

  • TCP checksum strength possibly inadequate
  • IPsec message digest could be used for increased strength
  • Alternatively, a CRC for TCP?
  • Selective retransmission desirable
  • Possible use of SSL

/ TSL in security architecture

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SLIDE 14

05 J ul 2000 P age 14 R andy Haagens

Aggregation Alternatives

Proposed for iSCSI. Commands and status iSCSI messages are sequenced independently, in a central iSCSI module. O ther iSCSI functions can be delegated to the individual protocol stacks. M ultiple TCP/ IP engines operate independently.

TCP iSCSI iSCSI iSCSI iSCSI PHY IP LLC MAC TCP PHY IP LLC MAC TCP PHY IP LLC MAC TCP iSCSI PHY IP LLC MAC PHY IP LLC MAC PHY IP LLC MAC

TCP is modified to aggregate over multiple IP

  • addresses. That means that an end node can

have multiple IP addresses, and the TCP implementation is able to load balance across

  • them. Segments for the TCP connection frequently

arrive out of order at the several interfaces, but TCP puts them back in order using its sequence

  • numbers. Problem: TCP connections are currently

defined by the (IPaddr, Port, IPaddr, Port) 4-tuple. There is no TCP-layer connection ID to relate segments arriving on different IP addresses. Potential problem: O ne TCP engine must service all links, and could become a bottleneck. IP does the aggregation, balancing traffic over multiple links. Problem: current routers would have difficulty preserving parallel flows in the last hop, as they would tend to discover (through AR P) only

  • ne destination M AC address for a given IP

address.

TCP iSCSI IP LLC MAC LLC MAC LLC MAC PHY PHY PHY TCP iSCSI PHY IP LLC MAC PHY MAC PHY MAC

Effectively the same as above, with the additional problem that it adds a link dependency.

TCP iSCSI PHY IP LLC MAC PHY PHY

As specified by 802.3ad. Problem: frames for the same TCP connection will take the same link in a link bundle (so that they will arrive in order, which is not what’s desired here).

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SLIDE 15

August 10, 2000 P age 15 R andy Haagens

Other Issues

  • Topology discovery
  • Uses conventional IP endpoint discovery techniques
  • A means for discovering that an IP end point is an iSCSI node
  • A means of determining the IP connection topology within the end

node

  • A means for acquiring a list of valid targets
  • SCSI protocol-dependent means for discovering L

U topology

  • Security
  • Security requirements are discussed by Steve Bellovin in this session