iSCSI for Storage Networking

8/13/2019 iSCSI for Storage Networking

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SNIA IP Storage Forum White Paper iSCSI for Storage Networking

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Leverag ing th e Best f rom Storage AND Netwo rk ing

iSCSI builds on the two most widely used protocols from the storage and the networking worlds.

From the storage side, iSCSI uses the SCSI command set, the core storage commands usedthroughout all storage configurations.

On the networking side, iSCSI uses IP and Ethernet, which are the basis for most corporatenetworks, and are increasingly being used for metropolitan and wide area networking as well.

With almost 30 years of research, development and integration, IP networks provide the utmostin manageability, interoperability and cost-effectiveness.

Figure 2 shows how SCSI is mapped to TCP/IP through the iSCSI layer, freeing SCSI from itsparallel bus structure.

SCSI Core command set for hosts and device communication

TCP Layer Reliable delivery

iSCSI Layer Routable packaging (i.e. SCSI serialization) for network connectivity

Internet Protocol (TCP/IP)

Internet SCSI (iSCSI)

SCSI Command Set

SCSI Bus Protocol

Enterprise IP Network (SAN, LAN, MAN, WAN)

iSCSI is a standards track document in

the IETF that specified the serialization

of the SCSI command set to TCP/IP

IP Layer Universal connectivity to global IP infrastructure

Figure 2: Leveraging SCSI and IP for Storage Networking

IPIP

TCPTCP

iSCSIiSCSI

iSCSI Protocol Stack

Standard SCSI Command SetStandard SCSI Command Set

Operating SystemOperating System

ApplicationsApplications

Figure 3: The iSCSI

Protocol Stack

Figure 3 shows a simplified version of a protocol stack including iSCSI. Use of the standardSCSI command set facilitates interoperability with existing operating systems and applications

that lay above that layer. Additionally, use of a standard TCP/IP network provides universalreach to the global IP infrastructure.

Ad vantages of IP Storage

Familiar network technology and management

o Reduces training and staff costs Proven transport infrastructure

o Increases reliability

Transition from 1 Gigabit Ethernet to 10-Gigabit Ethernet and Beyond

o Protects investment with simplified performance upgrades

Scalability over long distances

o Enables remote data replication and disaster recovery

Brings Ethernet economics to storageo Enables lower total cost of ownership


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Elements of IP Storage NetworkingIP Storage Networking refers to computer systems and storage elements that are connected viaIP. It also refers to the IP infrastructure transporting storage traffic among these targets. Figure 4shows the various elements of an IP storage network.

The first element, Device I/O, refers to computer systems and storage resources that have nativeIP interfaces. These could include servers, disk arrays or tape libraries with an iSCSI adapter oriSCSI controller. These interfaces typically are Ethernet and include protocol processing, such asTCP/IP offload engines, to reduce processing loads on the host devices.

The second element of an iSCSI storage area network is the fabric of switches. The advantage of

an IP based fabric is that users can create a SAN using standard Ethernet switches and routers totransport data over the SAN fabric. The fabric also may include storage routers and switches thathave a combination of iSCSI interfaces and other storage interfaces such as SCSI or Fibre

Channel. Storage switches and routers provide multi-protocol connectivity not available inconventional IP and Ethernet switches. They also provide storage specific functionality, such as

peer-to-peer copy commands.

The third element of IP Storage networking is the SAN interconnection. Since iSCSI is a native

IP-based protocol, SAN interconnection does not require storage-specific functionality and canuse a shared or dedicated IP/Ethernet network.

Switch

Switch Switch

Switch

Switch

Switch Switch

Switch

Shared or Dedicated

IP based

LAN, MAN, WAN

Switch

Switch Switch

Switch

Device I/O

Device I/O

StorageArea

Network

SAN

Interconnect

Figure 4: Segments of Storage Networking

Unders tand ing End Sys tems

Given that an iSCSI environment can leverage existing IP networks, a significant portion of theoverall solution involves iSCSI end systems. Figure 5 outlines the significant functions of

traditional IP Network Interface Cards, traditional Storage Adapters, and new IP StorageAdapters.


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Network Interface Cards (NICs)Traditional NICs (Ethernet adapters in servers and PCs) are designed to transfer packetized file

level data among PCs, servers and storage devices, such as NAS appliances. However, NICs donot traditionally transfer block level data, which is handled by a storage host bus adapter, such as

Fibre Channel or parallel SCSI. In order for a NIC to process block level data the data needs to

be placed into a TCP/IP packet before being sent over the IP network. Through the use of iSCSIdrivers on the host or server, a NIC can transmit packets of block level data over an IP network.

When using a NIC, the server handles the packet creation of block level data and performs all ofthe TCP/IP processing. This is extremely CPU intensive and lowers the overall server

performance. The TCP/IP processing performance bottleneck has been the driving force behindthe development of TCP/IP offload engines (TOE) on adapter cards. A TOE removes the TCP/IPprocessing from the host CPU and completes TCP/IP processing and packet creation on the

HBA. Thus a TCP/IP offload storage NIC operates more like a storage HBA rather than astandard NIC.

Storage Host Bus Adapters (HBAs)Unlike NICs, Storage HBAs are designed to transmit block level data to and from storage

applications. A reference to the entire block is transferred from the application to the adapter,bypassing the need to break the block into smaller frames. However, because of this, the HBAmust handle the task of segmenting the block into frames, a process that takes place through a set

of specialized chips that enable the HBA to relieve the computer resources of the CPU for thisprocess. When it completes that task, the HBA forwards the frames.

iSCSI AdaptersiSCSI Adapters combine the functions of NICs with the function of a storage HBA. Theseadapters take the data in block form, handle the segmentation and processing on the adapter card

with TCP/IP processing engines, and then send the IP packets across an IP network. Theimplementation of these functions enables users to create an IP based SAN without lowering theperformance of the server. In advance of the introduction of iSCSI adapters, some vendors

released software versions of these adapters. These software-enabled adapters accept block leveldata from applications, but still require CPU cycles for the TCP/IP processing. The advantage of

such adapters is that they can work on existing Ethernet NICs. The main disadvantage is thatthey require heavy CPU utilization for TCP/IP processing.

Application

Layer

LinkLayer

Network Interface CardLAN traffic, NAS

Driver

Layer

FileFile

IPPacket

IPPacket

IPPacket

IPPacket

IP

Packet

IP

Packet

IP Server

On Ethernet

IP

Packet

IP

Packet

IP

Packet

Storage HBAFC storage traffic

BlockBlock

FC Server

On Fibre Channel

FC

Frame

FC

Frame

FC

Frame

iSCSI AdapterIP Storage traffic

BlockBlock

IP Server

On Ethernet

IP

Packet

IP

Packet

IP

Packet

BlockBlock BlockBlock

Figure 5: Network Interface Cards and Host Bus Adapters


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Deployment Scenarios for iSCSI

Bu i ld ing New Nat ive iSCSI Storage Netwo rks

Data Center ApproachAn iSCSI SAN is a perfect choice for a user interested in moving to networked storage. Using

the same block level SCSI commands as direct attach storage, iSCSI provides compatibility withuser applications such as file systems, databases, and web serving. Similarly, since iSCSI runs onubiquitous and familiar IP networks, there is no need to learn a new networking infrastructure to

realize SAN benefits. To build an iSCSI storage network in a data center, iSCSI host busadapters can be used in servers, along with iSCSI storage devices and a combination of IP and

Ethernet switches. IP Storage switches and routers can be used if required. Figure 6 shows aprimary data center iSCSI storage network connecting to remote sites.

Expanding iSCSI Storage Networks to Metro and Wide Area Networks

The rapid adoption and expansion of IP data on the Internet has proven the viability of using IPacross long distance wide area networks. Although it is expected that initial deployments ofiSCSI will use private networks, the use of IPs security infrastructure (such as IPSec and SSL toprovide authentication and privacy) it will be possible to use public networks for wide area

iSCSI storage traffic as well.

IP

MAN/WAN

iSCSI provides a native IP link to

Metropolitan and Wide Area

Networks (MANs / WANs)

Primary Data Center

iSCSI Storage Network

Secondary Data Center


Storage Service Provider


IP Switch

IP Switch IP Switch

IP Switch

iSCSI

iSCSI

iSCSI

iSCSI

iSCSI

iSCSI

IP Switch

IP Switch IP Switch

IP Switch

iSCSI

iSCSI

iSCSI

iSCSI

iSCSI

iSCSI

IP Switch

IP Switch IP Switch

IP Switch

iSCSI

iSCSI

iSCSI

iSCSI

iSCSI

iSCSI

Shared or Dedicated

IP Network

iSCSI Storage

Devices

iSCSI Servers

Figure 6: Data Center iSCSI Storage Networks Offer Seamless MAN/WAN Access

Applications for Native iSCSI storage networksWith a native iSCSI storage network, customers can benefit from the following applications in

the data center

Server and storage consolidationWith a networked storage infrastructure, customers can link multiple storage devices to

multiple servers allowing for better resource utilization, ease of storage management, andsimpler expansion of the storage infrastructure.


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Applications for linking iSCSI to Fibre Channel

IP Access to Storage / Storage Consolidation

Using iSCSI Adapters in servers, customers can now provide access to FC storage

resources across an IP network. This greatly expands storage access flexibility, allowingcustomers to consolidate FC storage without limiting access to servers. Databaseinformation, for example, can be directly accessed from servers across an IP network.

Remote Backup for Enterprise CustomersWith the ability to use IP networks, the combination of iSCSI and IP Storage routers or

switches enables remote backup for enterprise customers. Remote sites can operateindependently, yet still benefit from enterprise storage resources for iSCSI server to FCstorage backup and recovery. This application allows data center managers to centralize

corporate data resources in one location while providing sophisticated enterprise storagemanagement to several remote customers at different sites.

ConclusioniSCSI will expand the market for networked storage by giving IT managers another alternative to

direct attached storage that delivers the advantages of networked storage. IP storage networkstake advantage of IP networking knowledge in IT departments and use existing networkmanagement and tools for LANs, MANs and WANs today. Riding the IP wave of technology

development and enhancements like the introduction of 10 Gigabit Ethernet, iSCSI provides alogical unified infrastructure development path for corporations and service providers alike.

Acknowledgements

Author: Gary OrensteinContributors: Chris Humphrey, Bryce Mackin, Graeme Plant, Ahmad Zamer

iSCSI for Storage Networking

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