Basics of Bus Standards In Storage Technology Network

Sheel Sindhu ManoharIWC2013011Mtech (WCC)

Indian Institute of Information & Technology, Allahabad

IO Techniques

For the transfer of the Data

● ChannelThe faster you switch the clock the more is the speed

● Controller● Protocols

Due to some physical characterstics the bits not reach at the destinaton due to large distance not at same time on different channel. The more the distance more the data not to be synchronized.

In the parallel data transfer→ At large distance → loss of sync.(CLK SKEW) → Bits not reach together(on different channels)

→ Clock skew limits the length of the bus

In case of LIMITED LENGTH

→ Limits the number of devices→ Restricts remote mirroring

Increase The Length

● Use distinct network protocols

→ Ethernet(LAN)

→ TCP/IP(Public N/W)

● Optical Fibre

→ Large bandwidth

→ Seriel transmission

● Disadvantage → Costly

Entire protocol needs to be designed (All 7 Layers)

Bus Standards

● Transfer data – Data Bus (Data in block format)● Data Bus – Seriel/Parallel● Low BW – Parallel transfer 8/16/32/64 bits(low Bit Rate

is allowed)● Problem with parallel data transfer (need for tight sync)● Tx Id, Rx Id – Address memory

location for scalablity – Hierarchical Addressing● In band/Out of band control signalings● For maintanance (change mgment)● Unit of transfer

Control Signalling

● Tx – Initiators Rx – Targets

● Control Signaling – Daisy Chaining out of band control signaling

● Tx, Rx – AdressingLogical Unit Addressing } LUN

● Data bus – Parallel

Data Bus Parallel

● Tight synchronising Request● Clock Skew problem which limits the maximum

distance

Clock Skew Problem

● Clock skew problem can be solved using fibre channel

● High bit rate and BandWidth● Seriel transmission● Overcome clock skew

Proposed Solution (clock skew)

● Requirement – High Data Transfer Rate

problem – clock skew(Distance bit rate trade off in parallel data transfer)

● Solution1: High BW ChannelSeriel data Transfer } Optical

FibreSupports – 1 to 2 Gbps

– Distances in Kms

Disadvantages in Using FC

● All new infrastructures● Also needs Backward compatiblity

Main Disadvantages in using Fibre Channel in Storage Area

Some other problems

● Problem1: Existing devices (CPU rate) Understand LUN (SCSI Targets) & transfer data in blocksSolution – Interface (Performs SCSI<-> FC standards)

● Problem2: Costly to replace existing Infrstructures Solution1 – SCSI over the InternetSolution2 – Fibre Channel frames over TCP/IP

Tunneling

● Tunnel FC frame in the IP packets

– [iFCP] internet FCP (Intergateway data transfer)

– [FcoE] Fibre Channel over the switched ethernet

● SCSI (Commands + Data) can be transferred by encapsulating in IP datagram. This is used in the iSCSI network