i SCSI Past Present Future Robert Russell Computer

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i. SCSI: Past, Present, Future Robert Russell Computer Science Department and IOL University of

i. SCSI: Past, Present, Future Robert Russell Computer Science Department and IOL University of New Hampshire © UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY

Very Brief History • Late 1997 – idea of storage over IP – Julian

Very Brief History • Late 1997 – idea of storage over IP – Julian Satran, IBM research • Late 1999 – IBM and Cisco start joint work on proposal for standard • Early 2000 – IETF creates IP storage working group • November 2000 – IETF draft 0 posted UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Rest of Brief History • Jan 2001 – SNIA creates IP storage forum •

Rest of Brief History • Jan 2001 – SNIA creates IP storage forum • July 2001 – first UNH IOL i. SCSI Plugfest – 28 companies attended – Tested drafts 0 and 6 • Feb 2003 – IETF approves draft 20 • June 2003 – Microsoft Server with i. SCSI • April 2004 – IETF publishes RFC 3720 UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Today – December 2005 • i. SCSI products offered by all storage and platform

Today – December 2005 • i. SCSI products offered by all storage and platform vendors • Many small vendors in the market • i. SCSI now well accepted at low and middle performance ranges • 1 Gig wire-speed HBAs available • 10 Gig i. SCSI products starting to appear UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Other SAN Technologies • Enterprise data centers still based on Fibre Channel (1 Gig,

Other SAN Technologies • Enterprise data centers still based on Fibre Channel (1 Gig, 2 Gig, soon 4 Gig) • Renewed interest in i. FCP and FCIP • Will Fibre Channel equipment prices be lower in the near future? ? • Infini. Band UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

SCSI Transport Protocol for TCP • Based on widely used, off-the-shelf technology – SCSI,

SCSI Transport Protocol for TCP • Based on widely used, off-the-shelf technology – SCSI, TCP, IPsec, Ethernet – Familiar, already installed infrastructure – Commodity components, inexpensive • Permits all-software implementations – Encourages experimentation, early feedback – Many freely distributed implementations UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI Design Principles • Target controls data transfer – To enable fair sharing

i. SCSI Design Principles • Target controls data transfer – To enable fair sharing of resources – To manage limited memory resources – To improve disk performance • Messages (PDUs) in both directions are sequenced and acknowledged – – In addition to TCP sequencing and acknowledging To maintain SCSI command ordering To detect errors To control data flow UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Text Negotiation • Stylistic departure from FC, TCP, etc. Key=value • Used

i. SCSI: Text Negotiation • Stylistic departure from FC, TCP, etc. Key=value • Used for multiple purposes: Login, authentication, discovery, renegotiation • Easy to use, understand, debug • Slower to process, bigger messages – Used mostly in Login – sessions are long-lived – Linux initiator now split between kernel/user UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Designed-in Extensibility • Text keys and values – Can carry info in

i. SCSI: Designed-in Extensibility • Text keys and values – Can carry info in both directions - slow • Additional header segments (AHS) – Can carry info from initiator to target - fast • Asynchronous messages – Can carry info from target to initiator - fast UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Error Handling • End-to-end CRCs (digests) useful because TCP has weak checksum

i. SCSI: Error Handling • End-to-end CRCs (digests) useful because TCP has weak checksum Stone and Partridge, ACM SIGCOMM 2000 pp 309 -319 • TCP checksum observed to catch error in every 1 in 1100 to 1 in 32000 segments • Error gets through TCP checksum to application every 1 in 6 million to 1 in 10 billion segments • Markers embedded in stream – little used • 3 levels of recovery to deal with CRC errors and connection loss UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Error Recovery • Complex, many choices of action to take • Poorly

i. SCSI: Error Recovery • Complex, many choices of action to take • Poorly tested, may hide bugs • Why so complex? – SCSI error recovery slow, crude – Some applications require absolute accuracy – Compromise after long discussion • Philosophy repudiated by i. SER/i. WARP UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Draft Implementer’s Guide • 3 clarifications – no change to existing code – Over/underflow,

Draft Implementer’s Guide • 3 clarifications – no change to existing code – Over/underflow, reserved ITT, format errors • 2 corrections – minor changes to existing code – Interaction between R 2 Ts on same connection – Handling data digest errors on Reject, Async messages UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Draft Implementer’s Guide • 2 new additions – minor changes to existing code –

Draft Implementer’s Guide • 2 new additions – minor changes to existing code – Task management effecting multiple I_T Nexi • New proposal now under discussion – Reinstating unnamed discovery sessions • To avoid interference with normal sessions • To permit independent discovery sessions based on target addresses UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Relatively Unused Features • Error recovery level 2 • Out of order PDUs and/or

Relatively Unused Features • Error recovery level 2 • Out of order PDUs and/or PDU sequences • Multiple connections (scheduling policies? ) • Use with IPsec (management) • Bidirectional commands (only 1 in SBC-2) • Additional header segments (AHS) • Markers UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: RFC 3720 Document • Long, informal English prose • Ambiguous, can be

i. SCSI: RFC 3720 Document • Long, informal English prose • Ambiguous, can be misinterpreted • Testing is long, has many combinations • Need for use of formal methods for specification, verification, testing Bishop et al. , ACM SIGCOMM 2005 pp 265 -276 Rigorous Specification for TCP and UDP UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Performance Factors • Workload characteristics – Sequential streaming vs random access –

i. SCSI: Performance Factors • Workload characteristics – Sequential streaming vs random access – Read/write, large/small transfers • Network characteristics – Speed (100, 10000 Mbps) – Distance (LAN, MAN, WAN) – Error rates – Congestion UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Performance Metrics • Bandwidth utilization – high is desirable • CPU utilization

i. SCSI: Performance Metrics • Bandwidth utilization – high is desirable • CPU utilization – low is desirable • Latency – low is desirable • Transaction rate – high is desirable UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Performance • Numerous studies done, many more to do • Many, many

i. SCSI: Performance • Numerous studies done, many more to do • Many, many tunable parameters at all levels – SCSI – i. SCSI – TCP – Ethernet • Interactions/tradeoffs within/between levels • Dynamic parameter adjustment UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

SCSI Initiator Parameters • Maximum no. of outstanding commands – Big enough to keep

SCSI Initiator Parameters • Maximum no. of outstanding commands – Big enough to keep network pipeline full • Maximum no. of sectors per command – Big to allow multi-sector requests • Maximum no. of I/O vectors per command – Big to allow scatter/gather operations • Coalescing contiguous blocks – In order to reduce need for I/O vectors UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Tunable Parameters • PDU size – declared on initiator and target –

i. SCSI: Tunable Parameters • PDU size – declared on initiator and target – Usage determined independently by sender – Big enough to keep pipeline full • Out-of-order PDUs – negotiate on/off – Usage determined independently by sender – May be useful when target sends Data. In PDUs – May be bad when initiator sends Data. Out PDUs UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Tunable Parameters • Header/data digests – negotiate on/off – Used by both

i. SCSI: Tunable Parameters • Header/data digests – negotiate on/off – Used by both sides – Catches errors that get through TCP checksum • Error recovery level – negotiate 0, 1 or 2 – Used by both sides – Higher levels give faster, smoother recovery • Markers – negotiate on/off and interval – Used by each side independently – Recovers PDU alignment in TCP stream UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Tunable Parameters • Immediate/unsolicited data – negotiate on/off and maximum – Usage

i. SCSI: Tunable Parameters • Immediate/unsolicited data – negotiate on/off and maximum – Usage determined by initiator on writes only – May reduce latency on small writes – May increase buffering on target – extra copy • Multiple connections – negotiate maximum – Creation and usage determined by initiator – Scheduling algorithms not yet explored UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Tunable Parameters • Burst sizes – negotiate max – Usage determined independently

i. SCSI: Tunable Parameters • Burst sizes – negotiate max – Usage determined independently by target – Big enough to keep pipeline full • Number outstanding R 2 Ts – negotiate max – Usage determined independently by target – Big enough to keep pipeline full UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Tunable Parameters • Phase collapse – internal to target – Eliminates extra

i. SCSI: Tunable Parameters • Phase collapse – internal to target – Eliminates extra response PDU from target • Command window – internal to target – Controls load and buffer usage on target – Big enough to keep pipeline full UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Tunable Parameters • A-bit, Data. Ack SNACK – negotiate ERL > 0

i. SCSI: Tunable Parameters • A-bit, Data. Ack SNACK – negotiate ERL > 0 – Usage determined independently by target on reads only – Reduces buffering on target • Out-of-order Sequences – negotiate on/off – Usage determined independently by target – Reduces latency and buffering on target UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

TCP: Tunable Parameters • Maximum window sizes – Bigger generally better • Options for

TCP: Tunable Parameters • Maximum window sizes – Bigger generally better • Options for timestamps, window scaling, etc. • Delayed, selective acknowledgements • Nagle algorithm – to coalesce small packets – Turn off except when streaming small PDUs • Dynamic packet coalescing – Better control than Nagle on/off UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Ethernet: Tunable Parameters • Jumbo frames – Improves bandwidth utilization – Decreases CPU overhead

Ethernet: Tunable Parameters • Jumbo frames – Improves bandwidth utilization – Decreases CPU overhead – Not supported on all NICs, HBAs, switches • Driver DMA input queue length – Bigger to smooth out traffic bursts • Interrupt coalescing – Trades response time against CPU overhead UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Tradeoff Example: i. SCSI CRC • Use of TOE without i. SCSI CRC off-loaded

Tradeoff Example: i. SCSI CRC • Use of TOE without i. SCSI CRC off-loaded – Reduces performance due to memory access • Use of TOE with i. SCSI CRC off-loaded – Reduces protection due to bus crossing • Use of TCP copy and i. SCSI CRC in software – Expensive, but performance better for small PDU UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI CRC in Software • 2% reduction for PDUs less than 2 KB

i. SCSI CRC in Software • 2% reduction for PDUs less than 2 KB • 31% reduction for PDUs bigger than 8 KB UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Graph of Parameter Interaction UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present,

Graph of Parameter Interaction UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Parameter Relationship • Let N = number of outstanding. R 2 Ts

i. SCSI: Parameter Relationship • Let N = number of outstanding. R 2 Ts • Let M = Max. Burst. Length (MRDSL) in KB • Then at top of the “knee” in the graph, N x M = 64 • The “pipeline size” at this latency • Target controls N to keep pipeline full • Formula needs additional factor for latency UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Equation for Write Throughput t = A*x 1 + B*x 2 + C*x 3

Equation for Write Throughput t = A*x 1 + B*x 2 + C*x 3 + D*x 4 + E*x 5 +F t = Time in msec to transmit one MB x 1 = Number of R 2 Ts /command x 2 = Number of data-outs /command x 3 = Immediate data bytes(MB) /command x 4 = Unsolicited data bytes(MB) /command x 5 = Solicited data bytes(MB) /command UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Calculated Coefficients A = 1. 82 msec / R 2 T PDU B =

Calculated Coefficients A = 1. 82 msec / R 2 T PDU B = 0. 011 msec / Data. Out PDU C = 115. 29 msec / immediate MB D = 120. 79 msec / unsolicited MB E = 87. 72 msec / solicited MB F = 0 msec UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Write From UNH Initiator Calculated time Observed time UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY

Write From UNH Initiator Calculated time Observed time UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Write From Windows Initiator UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present,

Write From Windows Initiator UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Memory a Critical i. SCSI Resource • Initiator Paging to an i. SCSI disk

Memory a Critical i. SCSI Resource • Initiator Paging to an i. SCSI disk – VM system MUST NOT block for memory – Without care, standard TCP stack will block for memory (buffers and control structures) – Without care, i. SCSI data path will block for memory • Target memory starvation – May get multiple commands at once – Must hold memory until receipt acknowledged – Acknowledgement may be delayed indefinitely – Target must send Nop. In or set A-bit on last Data. In UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: CPU Load • CPU utilization is not negligible – Biggest percent from

i. SCSI: CPU Load • CPU utilization is not negligible – Biggest percent from TCP/IP, not i. SCSI or SCSI – Standard TOE off-loading helps output – i. SCSI HBA off-loading helps input and output – Software i. SCSI CRC is expensive for large PDUs UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

CPU Overhead without HBA • Interrupt rate – 1500 byte frame every 12 microsecs

CPU Overhead without HBA • Interrupt rate – 1500 byte frame every 12 microsecs on 1 GE – 9000 byte frame every 5 microsecs on 10 GE • Frequent cache flushing • Extra copying – TOEs help mainly on output – Input requires intermediate TCP buffers or costly memory mapping UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. WARP • IETF Remote Direct Data Placement WG • Suite of protocols –

i. WARP • IETF Remote Direct Data Placement WG • Suite of protocols – RDMAP – to control DDP coherently – DDP – to segment and place data directly – MPA – to align frames in TCP stream – SCTP – to bypass MPA/TCP, map DDP onto IP • Implemented in RNIC – RDMA-aware NIC • For general use, not just i. SCSI/i. SER UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Stack With i. SER/i. WARP R N I C UNIVERSITY of NEW

i. SCSI: Stack With i. SER/i. WARP R N I C UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. WARP: RNIC Concepts • Manages large transfers without host CPU interaction • Fragments

i. WARP: RNIC Concepts • Manages large transfers without host CPU interaction • Fragments large transfers into TCP segments, each with extra headers • Avoids copying at both ends of the wire • Adds end-to-end CRC checking • Adds markers to handle out-of-order frames UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. WARP: RNIC Benefits • Substantially reduces host overhead – Fewer host interrupts •

i. WARP: RNIC Benefits • Substantially reduces host overhead – Fewer host interrupts • Once per transfer, not once per frame – Fewer host cache flushes – Less use of host memory space • No network buffers in host memory – Less use of host memory bus • One direct transfer between wire and memory • Better use of network bandwidth • Lower network latency UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. WARP Details • Untagged buffers for control frames – 20 -byte header plus

i. WARP Details • Untagged buffers for control frames – 20 -byte header plus 4 -byte CRC • Tagged buffers for data frames – 16 -byte header plus 4 -byte CRC • Uses IPsec for transmission security • Many other security requirements for RNIC • Error handling philosophy – terminate the connection! UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SER: i. SCSI Extensions for RDMA • Interface between i. SCSI and RDMA

i. SER: i. SCSI Extensions for RDMA • Interface between i. SCSI and RDMA • i. SER adds 12 -byte header to control PDUs • Makes i. SCSI independent of any protocol – RDMAP/DDP/MPA/TCP/IP – RDMAP/DDP/SCTP/IP – Infiniband – Others? (Myrinet? , Quadrics? ) UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SER: Concepts • Target controls data flow – i. SCSI read = target

i. SER: Concepts • Target controls data flow – i. SCSI read = target RDMA write – i. SCSI write = target RDMA read • 4 new keys • Old keys for digests, markers are irrelevant • Handling of i. SCSI PDUs – R 2 T, Data. Out PDUs replaced by RDMA read – Data. In PDUs replaced by RDMA write – All other PDUs carried by RDMA send UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI/i. SER/i. WARP Error Handling • Guaranteed reliable, in-order deliver • i. SER/i.

i. SCSI/i. SER/i. WARP Error Handling • Guaranteed reliable, in-order deliver • i. SER/i. WARP error terminates connection! • All i. SCSI error recovery levels possible • Level 1 reduced to almost nothing – Digest and sequence errors now impossible – PDU retransmission timeouts discouraged – SNACK must no longer be sent UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Sharing a Target Device üMultiple hosts easily access common target üEfficient block

i. SCSI: Sharing a Target Device üMultiple hosts easily access common target üEfficient block transport directly to disk x No notion of files, directories, data, or metadata x No contention detection or resolution x No allocation or management of blocks UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Object-based Storage System • Idea: push more intelligence onto disk unit – Target manages

Object-based Storage System • Idea: push more intelligence onto disk unit – Target manages block allocation – Target defines objects and maps their blocks – Target manages object metadata • Enhancements to SCSI command set • Must rewrite file systems to use objects UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

ANSI Project T 10/1355 -D • SCSI Object-Based Storage Device Commands • Final Revision

ANSI Project T 10/1355 -D • SCSI Object-Based Storage Device Commands • Final Revision 10, 30 July 2004 “To provide efficient operation of I/O logical units that manage the allocation, placement and accessing of variable-size data-storage containers called objects. ” UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Object-store • All OSD commands are bi-directional • 200 -byte CDB requires

i. SCSI: Object-store • All OSD commands are bi-directional • 200 -byte CDB requires use of i. SCSI AHS – Reading a PDU header requires 2 steps: • Read 48 -byte Basic header, extract AHSLength • Read following AHSLength bytes – Header digest (CRC) is problematic • Use AHSLength value to read AHS headers and CRC • Use CRC to check complete header after read done • If AHSLength has error – input may block! UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Tracking SCSI Standards • i. SCSI version 0 (RFC 3720) based on: – SAM-2

Tracking SCSI Standards • i. SCSI version 0 (RFC 3720) based on: – SAM-2 Final revision 24, 11 -September-2002 – SBC Final revision 8, 13 -November-1997 • Upgrade to SAM-3 project T 10/1561 -D? – Final revision 14, 21 -September-2004 • SAM-4 project T 10/1683 -D – Current draft 3, 20 -September-2005 • Upgrade to SBC-2 project T 10/1417 -D? – Final revision 16, 13 -November-2004 UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

SCSI: SAM-3 Changes • Task management command changes • Async event notification removed •

SCSI: SAM-3 Changes • Task management command changes • Async event notification removed • Contingent allegiance removed • Untagged tasks removed • Task priority added UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Research Areas • Dynamic parameter adjustment – Respond to changes in application

i. SCSI: Research Areas • Dynamic parameter adjustment – Respond to changes in application load – Respond to changes in network conditions • Using parameters between levels – E. g. , let i. SCSI use TCP’s RTT to keep pipe full • Negotiate limits but operate at other values – Target controls burst sizes, outstanding R 2 Ts – Initiator controls connections, unsolicited data UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Research Areas • Scheduling multiple connections in session – What criteria to

i. SCSI: Research Areas • Scheduling multiple connections in session – What criteria to use? – Let different connections carry different info? • Reinstating sessions in order to renegotiate – Only limited differences between connections • New file systems • New caching schemes UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

i. SCSI: Novel Uses • Take advantage of extensibility features • Use AHS to

i. SCSI: Novel Uses • Take advantage of extensibility features • Use AHS to carry extra information with commands from Initiator to Target • Use Async messages to carry extra information from Target to Initiator • Use new text keys to exchange metadata • Use multiple connections to carry different information UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future

Initiator Target Applications New File System Disk SCSI i. SCSI Session i. SCSI TCP/IP

Initiator Target Applications New File System Disk SCSI i. SCSI Session i. SCSI TCP/IP Link UNIVERSITY of NEW HAMPSHIRE INTEROPERABILITY LABORATORY i. SCSI: Past, Present, Future