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Lecture Notes

Storage Area Netw ork( Unit - V)

M s. M adhu G. M ulge( M-Tech CSE )

M.B.E.'S College of Engineering, Ambejogai.

1ME - CSE [SAN- Unit V]

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ME - CSE [SAN- Unit V] 2

Application Studies

Although storage networks share common components in the form of servers, storage,

and interconnection devices, the configuration of a SAN is determined by the upper-layer

application it supports.

A SAN originally designed for a high-bandwidth application, for example, can also

facilitate a more efficient tape backup solution.

A post-production video editing application may have different requirements than ahigh-availability OLTP (on-line transaction processing) application.

Server-free tape backup applications may employ unique hardware and software

products that would not appear in a SAN designed to support server clustering.

Because SANs offer the flexibility of networking, however, you can satisfy the needs of

multiple applications within a single shared storage configuration.

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Full-m otion video

One of the first applications to employ high-performance SAN technology, full-motion

video editing leverages the bandwidth, distance, and shared resources that SAN technologyenables.

Digitized video has several unique requirements that exceed the capabilities of legacy

data transports, including the sustained transmission of multiple gigabit streams and

intolerance for disruption or delays.

Most SAN-based video applications use the SCSI-3 protocol to move data from disk to

workstations, although custom configurations have been engineered using IP for multicast

and broadcast distribution.

Video applications have common high-performance transport requirements but may vary

considerably in content.

A video editing application can center on a workgroup configuration.

Allowing peer workstations to access and modify video streams from one or more disk

arrays.

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In addition to the physical SAN topology, any application that allows data sharing must

have software support for file access and locking by multiple users.

A video broadcast application that serves content from a central data source to multiplefeeds must have the means to support multicast across the SAN.

Video used for training applications may support both editing workstations and user

stations, with random access to shared video clips or to instructional modules digitized on

disk.

In this example, the bandwidth required per workstation depends on the type of video

streams retrieved from and stored to disk.

Standard digitized streams may require ~30MBps throughput, whereas high-definition

video requires ~130MBps.

In the latter case, 2Gbps Fibre Channel would support ~400MBps full duplex, orsufficient bandwidth for a high-definition video stream to be read from disk, processed,

and written back concurrently.

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Fig: A peer video editing SAN via a switched fabric

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The configuration shows dual path in between the video editing workstations and

redundant SAN switches.

Device drivers for the host adapter cards must therefore support failover in case a link orswitch is lost, and preferably load balancing to fully utilize both paths during normal

operation.

In addition, the ratio of server to storage links must be adequate to support concurrent

operation by all workstations.

Larger storage arrays support multiple links so that a non-blocking configuration can be

built.

Video editing applications are intolerant of latency or delays. For optimal jitter-free

performance, video data can be written to the outer tracks of individual disks within the

storage array.

Although this technique reduces the total usable capacity, it requires less disk head

movement for reading and writing data and thus minimizes latency in disk performance.

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LAN-Free a nd Ser ver-Free Tape B ackup

Traditional parallel SCSI methods based on disk arrays are bound to individual servers,

tape backup options are limited to server-attached tape subsystems or transport of backupdata as files across the messaging network.

Provisioning each server with its own tape backup system is expensive and requires

additional overhead for administration of scheduling and tape rotation on multiple tape

units.

Performing backups across the production LAN allows for the centralization ofadministration to one or more large tape subsystems, but it burdens the messaging

network with much higher traffic volumes during backup operations.

When the volume of data exceeds the allowable backup window and stresses the

bandwidth capacity of the messaging network, either the bandwidth of the messaging

network must be increased or the backup data must be partitioned from the messagingnetwork.

Thus, the potential conflict between user traffic and storage backup requirements can be

resolved only by isolating each on a separate network, either by installing separate SAN

interconnection

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Fig: Tape backup across a departmental network with direct-attached storage

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Fig: Transitional LAN-free backup implementation for direct-attached storage

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Fig: LAN-free and server-free tape backup with SAN-attached storage

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Server Clustering

As enterprise applications have shifted from mainframe and midrange systems to

application and file servers.

More sophisticated designs that offer dual power supplies, dual LAN interfaces, multiple

processors, and other featuresto enhance performance and availability.

The potential failure of an individual component within a server is thus accommodated

by using redundancy.

Redundancy typically implies hardware features but may also include redundant

software components, including applications.

Redundancy can also be provided simply by duplicating the servers themselves, with

multiple servers running identical applications.

In the case of failure of a hardware or software module within a server, you shift users

from the failed server to one or more servers in a server cluster.

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The software used to reassign users from one server to another with minimal disruption

to applications is necessarily complex.

Clustering software written for high-availability implementations can be triggered bythe failure of a hardware, protocol, or application component.

The recovery process must preserve user network addressing, login information,

current status, open applications, open files, and so on.

Clustering software may also include the ability to balance the load among active

servers.

In this way, in addition to failover support, the servers in a cluster can be maximized to

increase overall performance.

SANs allow server clusters to scale to very large shared data configurations, with more

than a hundred servers in a single cluster.

The clustering software determines which components or applications on each server

should be covered by a failure, subsets of recovery policies can be defined within the

server cluster.

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Intern et Service ProvidersInternet service providers that provide Web hosting services have traditionally

implemented servers with internal or SCSI-attached storage.

For smaller ISPs, internal or direct-attached disks are sufficient as long as storage

requirements do not exceed the capacity of those devices.

For larger ISPs hosting multiple sites, storage requirements may exceed the SCSI-

attached capacity of individual servers.

Network-Attached Storage (NAS) or SANs are viable options for supplying additional

data storage for these configurations.

In addition to meeting storage needs, maintaining availability of Web services is critical

for ISP operations.

Because access to a Web site (URL) is based on Domain Name System (DNS) addressing

rather than physical addressing, you can deploy redundant Web servers as a failover

strategy.

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If a primary server fails, another server can assume access responsibility via round-robin

DNS address resolution.

For sites that rely on internal or SCSI-attached storage, this technique implies that eachserver and its attached storage must maintain a duplicate copy of data.

This solution is workable so long as the data itself is not dynamicthat is, it consists

primarily of read-only information.

This option is less attractive, however, for e-commerce applications, which must

constantly update user data, on-line orders, and inventory tracking information.

The shift from read-mostly to more dynamic read/write requirements encourages the

separation of storage from individual servers.

With NAS or SAN-attached disk arrays, data is more easily mirrored for redundancy and

is made available to multiple servers for failover operation.

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Fig: A small ISP implementation using network-attached storage

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SAN architecture brings additional benefits to ISP configurations by providing high-

speed data access between servers and storage using block I/O instead of NFS or CIFS file

protocols and by enabling scalability to much higher populations of servers.

you can extend the SAN with additional switch ports to accommodate expansion of

storage capacity and increased population of Web servers.

This small configuration can scale to hundreds of servers and terabytes of data with no

degradation of service.

Fig [a] depicts a scalable ISP configuration using iSCSI for block I/O access to storage

and tape.

In this case, the Ethernet switch is a common interconnection both for Web traffic via

the IP router and for block access to storage data.

Although servers can be provisioned with dual Ethernet links to segregate file and blocktraffic using VLANs, some iSCSI adapters support file and block I/O on the same

interface.

Depending on bandwidth requirements, this solution may minimize components and

wiring and simplify the configuration.

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Fig [a]: ISP configuration built with iSCSI

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Fig [b]: ISP configuration built with Fibre Channel

Figure [b] shows the functional equivalent to (a) but uses Fibre Channel instead of iSCSI.

This configuration introduces additional devices and connections but fulfills the requirement

for high performance and scalable access to shared storage resources.

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Campus Storage Netw orks

The need to share storage resources over campus or metropolitan distances has been one

by product of the proliferation of SANs on a departmental basis.

Separate departments within a company, for example, may make their own server and

storage acquisitions from their vendor of choice.

Each departmental SAN island is designed to support specific upper layer applications,

and so they may be composed of various server platforms, SAN interconnections, andstorage devices.

It may be desirable, however, to begin linking SANs to streamline tape backup

operations, share storage capacity, or share storage data itself.

Creating a campus network thus requires transport of block storage traffic over

distance as well as accommodation of potentially heterogeneous SAN interconnections.

Fibre Channel supports distances of as much as 10 kilometers over single-mode fiber-

optic cabling and long-wave transceivers.

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This is sufficient for many campus requirements, but to drive longer distances requires

additional equipment.

The main issue with native Fibre Channel SAN extension is not the distance itself but therequirement for dedicated fiber from one site to another.

Many campus and metropolitan networks may already have Gigabit Ethernet links in

place, but to share the same cable by Fibre Channel and Gigabit Ethernet simultaneously

requires the additional cost of dense wave division multiplexing (DWDM) equipment.

Connecting Fibre Channel switches builds a single layer 2 fabric, and therefore multiplesites in a campus or metro storage network must act in concert to satisfy fabric

requirements a campus storage network with a heterogeneous mix of Fibre Channel and

iSCSI-based SANs.

Example, existing Gigabit Ethernet links connect the various buildings.

Depending on bandwidth requirements, these links can be shared with messaging traffic

or can be dedicated to storage.

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For Fibre Channel SAN connectivity, FCIP could be used, but this example shows

iFCP gateways to ensure autonomy of each departmental SAN and isolation from

potential fabric disruption.

The administrative building is shown with aggregated Gigabit Ethernet links to the data

center to provide higher bandwidth, although 10Gbps Ethernet could also be used if

desired.

The development center is shown with an iSCSI SAN, which requires only a local

Gigabit Ethernet switch to provide connections to server, storage, and the campus.

This campus configuration could support multiple concurrent storage applications,

such as consolidated tape backup to the data center or sharing of storage capacity

between sites.

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Fig: Remote tape vaulting from branch offices to a regional data center

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Disaster Recovery

Like tape backup operations,disaster recovery (DR) has been viewed as a necessary but

unattractive requirement for IT storage strategies.

The cost of implementing a DR solution is balanced against both the likelihood of a

major disruption and the impact on business if access to corporate data is lost.

Disaster recovery tends to move toward the top of IT priorities only after

major natural or human-caused disasters.

The scope of a DR solution is more manageable if administrators first identify the types

of applications and data that are most critical to business continuance.

Customer information and current transactions, for example, must be readily accessible

to continue business operations.

Project planning data or code for application updates is not as mission critical, even

though such code may represent a substantial investment and should be recovered at

some point.

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Reducing the volume of data that must be accessible in the event of disaster is key to

sizing a DR solution to capture what is both essential and affordable.

Another fundamental challenge for DR strategies is to determine what distance issufficient to safeguard corporate data.

Performance problems beyond a metro circumference make native Fibre Channel

extension unsuitable for robust DR scenarios.

FCIP and iFCP can provide long distance support for Fibre Channel-originated storage

traffic, whereas iSCSI offers a native IP storage solution to address the distance issue.

The maximum distance allowed depends on the type of DR strategy to be implemented.

DR supports both data replication and tape backup options and uses IP network services

to connect the primary site to the DR site.

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Fig: Disaster recovery configuration using IP network services and disk-based data replication

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Thank U ~!~

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