This chapter examines how storage-area networks (SAN) enable customers to interconnect data centers, provide continu-ity, provide storage consolidation, and unify storage management.
An Overview of SAN Components and Technologies
SAN technologies enable organizations to maximize their storage capacity through a unified set of components and archi-tecture. A SAN solution can separate storage from the traditional server, and can share storage among multiple servers.
SANs also has a lower total cost of ownership (TCO) than direct-attached storage and can provide high I/O throughout via high-performance interconnect. One limiting factor to be aware of is that there may be limited vendor interoperability.
SAN main components:
n Host bus adapter (HBA): Provides connectivity between the host server and a storage device.
n Data storage devices: May be hard disks based on any one of the following technologies: SCSI, Fibre Channel, ATA, IDE, or Serial ATA.
n Storage subsystems: Examples of subsystems include the following:
n Just a bunch of disks (JBOD): A simple disk array.
n Storage arrays: A group of devices that provide mass storage and other functions and services.
n Redundant array of independent disks (RAID): RAID technologies allow disk drives to be combined and configured to provide increased performance and fault tolerance.
Overview of RAID: RAID arrays can be used to provide fault tolerance by mirroring data or through implementing parity check operations.
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Storage-Area Network Design
Primary RAID levels:
n RAID 0: Striping: Multiple disks are combined to form a single large volume. No fault tolerance is provided.
n RAID 1: Mirroring: Data is duplicated across two or more disks.
n RAID 3: Error detection: Data is striped across multiple disks and error-correction information is maintained by a dedicated disk drive.
n RAID 5: Error correction: Data and parity information, is striped across multiple disks.
Direct-attached storage features: Storage devices connect directly to the server. Storage has limited mobility because it is captive behind the server. It also has limited scalability because of limited devices.
Network-attached storage features: Storage devices are attached to the IP network (network-attached storage, NAS) allowing storage devices to be shared between servers and making it possible for files to be shared by users.
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IP LAN/WAN Network Attached Storage (NAS)
Servers NAS Devices
Data is transferred in IP packets.
FIGURE 6-1 Network-attached storage
CCDP ARCH Quick Reference
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Overview of SAN technologies:
n Small Computer System Interface (SCSI): A parallel interface technology used by hosts to attach peripheral devices.
n Fibre Channel: A serial data transfer architecture that provides a very high level of scalability and bandwidth that can be used to extend and network SCSI. This uses a point-to-point communication model facilitated by device login.
Virtual SAN (VSAN): Provides isolation among multiple devices that are physically connected to the same fabric. Inter-VSAN routing (IVR) can be used to allow sharing of centralized storage services, such as disks or tape libraries, across VSAN fabrics without the need to merge VSANs.
Fabric Shortest Path First (FSPF): A path-selection protocol used by Fibre Channel fabrics. Supports multipath routing and bases path status on a link-state protocol. Used by IVR to calculate the best path to a remote fabric.
Zoning: A logical groping of fabric connected devices within a SAN or VSAN, and can be used to enable access between an initiator and the storage target.
Fiber Connectivity (FICON): This upper-layer protocol was developed by IBM, and it uses the lower layers of Fibre Channel transport to facilitate connecting IBM mainframes with control units.
SANTap: An Intelligent Storage Service feature supported on the Storage Services Module (SSM), it enables data to be duplicated at another virtual initiator. This allows third-party data storage applications (for example, long-distance repli-cation, continuous backup, and so on) to be integrated into the SAN.
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Storage-Area Network Design
Design Considerations for SAN and SAN Extension
A SAN design should take into account the following considerations:
n Network topology should take into account the number of ports needed both today and in the future.
n End-to-end performance and throughput level should be central to the design.
n Business requirements for continuity and disaster recovery should guide the establishment of the necessary connec-tivity with remote data centers.
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Physical Topology
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SAN design should be based on a number of factors, including the following:
n Topology requirements and port density n Traffic management
n Stability and convergence n Fault isolation
n Oversubscription of devices
Benefits of the Cisco MDS 9000 family: SAN consolidation using VSANs, comprehensive security, and simplified SAN management.
Collapsed core design:
n Single-switch design: Provides 100 percent port design efficiency with a generally lower subscription ratio, while allowing empty slots to support future growth.
n Small-scale dual fabric: A small SAN with 48-port modules can provide a cost-effective solution with VLAN support and PortChannels with high availability to other switches allowing for future growth.
n Medium-scale dual fabric: Implemented using dual Director switches, it provides up to 528 ports per fabric.
Provides VLAN support, along with port bandwidth reservations to guarantee performance for those devices that require it and PortChannels with high availability to other switches to allow for future growth.
n Large-scale dual fabric: Leverages 48-port modules with port bandwidth reservations providing VLAN support, and uses port bandwidth reservations to guarantee performance for those devices requiring it. Each core switch (2) in this design supports 128 storage ports, and each edge switch (4) supports 496 host ports for a SAN system that supports a total of 1984 host ports across 256 storage ports resulting in a 7.75:1 ratio of hosts to storage.
Transporting storage traffic with SAN extensions: Multiple protocols and transport stacks can be used by SAN to transfer SCSI commands and data. Fibre Channel over IP (FCIP) and SCSI over IP (iSCSI) support block-level storage for remote devices and are both used to carry SCSI commands and status.
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CCDP ARCH Quick Reference
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Storage-Area Network Design
FCIP: A standards-based protocol (RFC 3821) primarily used for SAN extension across a WAN. FCIP is used to enable storage applications such as asynchronous data replication, disaster recovery, remote tape vaulting, and host initiator to remote pooled storage to be deployed without regard to latency and distance.
iSCSI: Can be used to carry SCSI commands, responses, and data over an IP network rather than over Fibre Channel.
Advantages of iSCSI versus FCIP:
n Supports standard networking equipment.
n Provides lower overall cost of ownership.
n Standards-based protocol (RFC 3720).
n TCP Offload Engine (TOE) can be used to scale iSCSI.
Advances in SAN extension:
n Tape acceleration: Used to speed up the I/O transactions during remote backups
n FCIP write acceleration: Increases I/O transactions between disk-based storage devices such as a disk array and servers
n Hardware-assisted data compression over FCIP: Provides extremely high data compression rates across WANs n Hardware-based IP Security (IPsec) encryption: Provides secure SAN extension transactions
High-availability SAN extension: Dual fabrics such as a yellow VSAN and a blue VSAN have been used to support high availability. PortChannels and optical protection schemes can be used to further augment the design and offer an addi-tional level of network protection.
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CCDP ARCH Quick Reference By Kevin Wallace, Michael Watkins ISBN: 9781587054990 Publisher: Cisco Press
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This PDF is exclusively for your use in accordance with the Safari Terms of Service. No part of it may be reproduced or transmitted in any form by any means without the prior written permission for reprints and excerpts from the publisher. Redistribution or other use that violates the fair use priviledge under U.S. copyright laws (see 17 USC107) or that otherwise violates the Safari Terms of Service is strictly prohibited.