Storage Area Networks; Unclogging
`LANs and Improving Data
`Accessibility
`
`"This important technology is moving into
`
`the mainstream in distributed networking
`
`and will be the normal, adopted way of
`
`attaching and sharing storage in a few
`
`short years."
`
`Michael Peterson,
`
`Strategic Research Corporation
`
`Kevin J. Smith
`
`Mylex Corporation
`
`Fremont, CA
`
`White Paper
`
`WPO30898.doc
`
`IBM-Oracle 1006
`Page 1 of 22
`
`

`

`Table of Contents
`
`Executive Summary ................................................................................................................................. 2
`
`Server-Dependent or Server-Independent Storage ................................................................................ 3
`
`SAN Taxonomy ....................................................................................................................................... 4
`
`Fibre Channel SAN’s ............................................................................................................................... 6
`
`SAN’s and Clusters .................................................................................................................................. 9
`
`SAN’s and NAS ..................................................................................................................................... 10
`
`SAN-Attached RAID Array Requirements ............................................................................................. 11
`
`Mylex External Array SAN Controllers ................................................................................................... 14
`
`Mylex Product Line SAN Features ........................................................................................................ 15
`
`References
`
`Copies of this and other white papers may be obtained from the Mylex web site
`(www.Mylex.com).
`
`RAID Controllers Are Not Created Equal;
`Many Will Not Survive on Wolfpack-fl Clusters
`
`DAC960PJ/PR Two Node Clustering
`
`Legal Notice
`
`ServerNet is a registered trademark of Tandem Computer Incorporated.
`VAXClusters is a registered trademark of Digital Equipment Corporation.
`NetWare is a registered trademark of Novell.
`Windows NT Server is a registered trademark of Microsoft.
`ESCON and SSA are registered trademarks of IBM.
`
`Other product names mentioned herein may be trademarks and/or registered trademarks
`of their respective companies.
`
`5/29/98
`
`IBM-Oracle 1006
`Page 2 of 22
`
`

`

`The key challenges facing IS executives are satisfying increasingly diverse networking
`requirements and reducing network complexity to lower total cost of ownership (TCO).
`Success depends on efficiently delivering:
`
`¯
`Hi.qh bandwidth for warehousing and web-based applications, i.e. multimedia,
`¯
`Low, predictable latency for time-sensitive applications, e.g. video conferencing,
`¯ Performance and resiliency for mission critical applications, e.g. OLTP.
`
`When computing resources were used only for internal operations, the cost of information
`bottlenecks and network failures was limited to lost productivity. However, as computing
`resources are used to engage customers, as well as manage operations, bottlenecks and
`network failures translate into lost business and lost productivity.
`
`A primary benefit of Storage Area Networks (SAN’s) is unclogging network arteries by
`moving bulk data transfers off client networks and onto specialized sub-networks, often
`referred to as the networks behind the servers.
`
`Figure 1. LAN’s and SAN’s
`
`With SAN’s, pools of storage (and related traffic) are removed from the LAN, externalized
`and shared by mainframes, UNIX and PC servers. In addition to de-congesting client
`networks, cross-platform data sharing and amortizing storage costs across servers, a SAN
`topology adds value by providing:
`
`¯
`Flexible, modular expansion by de-coupling server and storage investments,
`¯ Bandwidth and capacity scaling by eliminating SCSI and PCI bottlenecks,
`¯
`Increased fault tolerance and availability with redundant paths to data,
`¯
`Increased application performance with multiple gigabit links to data,
`¯ Simplified systems integration and enriched storage management,
`¯
`Improved data protection and security through centralization, and
`¯
`Lower total cost-of-ownership (TCO).
`
`MYLEX
`
`IBM-Oracle 1006
`Page 3 of 22
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`

`

`Sewer-Dependent Storage
`A paradigm shift from centralized to distributed storage began in the 1980’s driven by
`peer-to-peer networks, inexpensive UNIX and PC servers and the notion that moving
`computing and storage resources closer to workgroups would increase productivity. The
`result was islands of computing and disparate networks tied together by gateways. IS
`managers were faced with multiple copies of inconsistent data, networks that were
`expensive to manage and corporate assets (data) that were difficult to access and
`vulnerable to intrusion. The AberdeenGroup, a respected market research firm, refers to
`this environment as server-dependent storage (Figure 4).
`
`Figure 2. Server-Dependent Storage
`
`Server-Independent Storage
`Emerging SAN technologies mirror today’s LAN technologies with gigabaud shared and
`dedicated bandwidth. The AberdeenGroup advises: "Unless enterprises view and
`implement storage as if it were part of a giant network across the enterprise, they will pay
`too much for their storage and will face extreme, labor-intensive difficulties in performing
`vital storage-related functions, such as managing the storage and backing up and moving
`critical data." While giant SAN’s may someday become a reality, local SAN’s with server-
`independent storage are being deployed today.
`
`SAN
`
`Figure 3. Server-Independent Storage
`
`MYLEX
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`

`

`SAN: Storage Area Network or System Area Network?
`
`SAN is one of the more overloaded acronyms in computer jargon; its meaning is context
`sensitive. To systems people, SAN means System Area Network, and to storage people,
`SAN means Storage Area Network. Some people consider both definitions synonymous.
`However, while System Area Network and Storage Area Network topologies can be
`similar or even identical, there is an important distinction between the two technologies.
`
`System Area Network
`
`A System Area Network is a specialized network used in clusters configurations for node-
`to-node, node-to-device (primarily disk), and device-to-device communications that
`provides both high bandwidth and low latency. Low latency is the distinguishing
`characteristic of a System Area Network. Short message latency across a System Area
`Network is generally less than 10 microseconds, an order of magnitude less than Fibre
`Channel or Gigabit Ethernet. Low latency is a prerequisite to high performance for
`applications distributed across cluster nodes, e.g. parallel DBMS’s. Instances of a
`distributed application in a cluster environment frequently exchange messages to
`synchronize program execution or access to shared resources. Most System Area
`Networks use proprietary protocols, however, this is expected to change when the Vl
`Architecture is introduced in 1999. The Vl Architecture is an interconnect-independent set
`of protocols and API’s that standardize the interface between OS’s and cluster
`interconnects. ServerNet developed by Tandem Corporation, and SCl, an ANSI standard
`implemented by Dolphin, are examples of System Area Networks. System Area Network
`technologies can also be used to implement Storage Area Networks.
`
`Storage Area Network
`
`A Storage Area Network can be designed with a specialized or standard networking
`technology, e.g. Fibre Channel. Its purpose is to provide high bandwidth connections
`between servers and storage devices, and between storage devices, e.g. storage arrays
`and tape libraries. The primary objective of Storage Area Networks is high bandwidth for
`moving large amounts of data; latency is a secondary consideration. Storage Area
`Networks have been implemented with ESCON and HIPPI interfaces, and more recently
`with SSA and Fibre Channel. They can be deployed in homogeneous, e.g. all UNIX
`servers, or heterogeneous environments, e.g. a mix of UNIX and NT servers, and can be
`local to servers or remote from servers and connected to other (remote) Storage Area
`Networks. They use standard channel protocols, such as SCSl riding on top of Fibre
`Channel. In Storage Area Networks, storage is de-coupled from servers and managed as
`an independent resource.
`
`Storage Area Networks can be configured in fabric topologies with switches to
`interconnect servers and devices or implemented in loop topologies with hubs to simplify
`cable management and increase loop resiliency.
`
`In this paper, SAN is used in the Storage Area Network context.
`
`MYLEX
`
`4
`
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`Page 5 of 22
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`

`

`Related Terminology
`
`SAN-Attached Storage (SAS)
`
`SAN-Attached Storage refers to shared storage devices connected to servers and
`possibly each other via a Storage Area Network (typically Fibre Channel or SSA in open
`system environments).
`
`Network-Attached Storage (NAS)
`
`Network-Attached Storage are devices that directly attach to client networks, typically an
`Ethernet LAN, and provide optimized file services to clients and servers on the network
`using standard file I/O protocols, such as NFS and SMB, and networking protocols, such
`as IP. These devices are essentially specialized servers that functions as a server in a
`client-server relationship with other network computers requesting file access. Mylex,
`Network Appliance and Auxpex NAS products are examples of leading-edge Network-
`Attached Storage devices.
`
`[Storage attached to application servers but not directly attached to a LAN is sometimes
`referred to as Network-Attached Storage. In a sense, this is true since clients can access
`server-dependent storage over the network. However, this is stretching the NAS definition
`since application servers are not optimized for file serving.]
`
`SAN Interconnects and Topologies
`
`SAN’s can be designed in switched fabrics or arbitrated loops. Fibre Channel is an ideal
`SAN interconnect because it provides scaleable performance with virtually unlimited
`addressing and can span campus-wide distances. Bus technologies, such as SCSl, are
`inappropriate due to bandwidth, distance and device attachment limitations.
`
`SAN Interconnect Devices
`
`Switches, hubs and routers are interconnect devices that can be employed to construct
`SAN networks. Switches are used in fabrics to provide scaleable performance. Hubs are
`deployed in loop configurations to simplify cable management and enhance fault
`tolerance. Routers are useful for interconnecting complex SAN’s, particularly over long
`distances for data vaulting or disaster protection applications.
`
`SAN Interfaces
`
`ESCON, SSA and Fibre Channel are candidate SAN interfaces. ESCON is the dominate
`interconnect in mainframe environments. SSA is a newer IBM technology with
`performance characteristics similar to Fibre Channel Arbitrated Loops and has become a
`popular SAN interconnect. However, Fibre Channel appears to be emerging as the
`defacto industry standard SAN interface based on the breath of vendor support and
`market acceptance.
`
`MYLEX
`
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`Page 6 of 22
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`

`

`Industry Standard
`
`Fibre Channel defines a set of high performance serial I/O protocols and interconnects for
`flexible data transfer. It was developed by an ANSI committee and is supported by over
`seventy system, networking and storage vendors. Fibre Channel was designed to:
`
`¯ Provide a common interface for transferring large amounts of data at high
`transmission rates and low error rates,
`¯ Enable the simultaneous use of different transport protocols, such as, SCSI and IP,
`over a common interface, and
`¯ Support multiple physical interfaces and transmission media with varying distance and
`cost characteristics.
`
`Networks and Channels
`
`Fibre Channel was designed to provide seamless integration between networks that
`connect users to servers and channels that connect storage to servers. Networks
`connects heterogeneous computers located anywhere in the world and enables them to
`communicate with one another at any point in time on a peer-to-peer basis.
`Consequently, networks use complex protocols to authenticate users, set up sessions,
`route data, correct errors and cope with unstructured environments. Complex protocols
`impose high overhead on network computers. Conversely, channels are employed in
`structured, predictable environments to connect storage and other devices to serves over
`distance limited, low error rate transmission paths.
`
`Fibre Channel has not been extensively deployed in networks; the cost of Fibre Channel
`hardware is high relative to 10/100 and Gigabit Ethernet, and network infrastructures are
`in place to support Ethernet. However, Fibre Channel is rapidly becoming a storage
`interconnect standard; it provides the bandwidth, distance and flexibility required for
`Storage Area Networks:
`
`¯
`
`Full duplex transmission at 25 MB/s and 100 MB/s at distances up to:
`¯
`25 meters between devices using video or mini-coax copper cable,
`¯
`500 meters between devices using multi-mode fibre cables, and
`¯
`10,000 meters using single mode fibre cables,
`¯
`Full duplex 200 MB/s and 400 MB/s data rates in the not too distant future,
`¯ Extended addressibility:
`¯
`126 devices on an arbitrated loop, and
`¯
`
`1,000’s of devices in switched fabrics,
`¯
`Low error rates and end-to-end error checking for high data integrity,
`¯ Optional redundancy for high availability,
`¯
`Low cost in arbitrated loop topologies, and
`¯ Scaleable bandwidth in switched fabric topologies.
`
`MYLEX
`
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`Page 7 of 22
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`

`

`Loops or Fabrics
`
`Fibre Channel devices, called nodes, have a single or multiple ports to communicate with
`other nodes. Today, most Fibre Channel Host Bus Adapters (HBA’s) provide a single port
`but HBA’s with dual ports are expected in the future. Each port has a pair of electrical (for
`copper cables) or optical transceivers (for fibre cables); one for transmitting data and the
`other for receiving data. The pair of conductors is referred to as a link. Fibre Channel
`nodes can be connected with a single link or dual links for fault tolerance.
`
`Storage Area Networks can be configured as arbitrated loops with bandwidth shared by
`nodes on the loops or as switched fabrics with dedicated bandwidth between
`communicating nodes.
`
`Fibre Channel Arbitrated Loops (FC-AL)
`
`In a FC-AL, nodes arbitrate to gain access to the loop and then pairs of nodes establish a
`logical point-to-point connection to exchange data; the other nodes on the loop act as
`repeaters. With FC-AL, bandwidth is constant and shared; only one pair of nodes on the
`loop can communicate at any point in time. FC-AL is similar in operation to other shared
`media networks, such as FDDI or Token Ring.
`
`Figure 4. Fibre Channel Arbitrated Loop and Fabric Topologies
`
`Fibre Channel Switched Fabrics
`
`In a switched topology, the full bandwidth of a link is available to pairs of communicating
`nodes and multiple pairs of nodes can simultaneously transmit and receive data. A._#s
`nodes are added to a switched configuration, the aggregate bandwidth of the network
`increases. The switch is an intelligent device that provides crossbar switching functions
`enabling multiple pairs of nodes to simultaneously communicate.
`
`MYLEX
`
`IBM-Oracle 1006
`Page 8 of 22
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`

`

`Hubs or Switches
`
`Hubs and switches are interconnect devices used in Storage Area Networks. They are
`available with advanced management capabilities similar to LAN management
`techniques; SNMP-based management is generally provided and some devices conform
`to the new Web-Based Enterprise Management (WBEM) standard. Hubs and switches
`can be cascaded to increase node connectivity; hubs up to the FC-AL limit of 126 nodes,
`and switches to thousands of nodes.
`
`Hubs
`
`Except for two node configurations connected in a point-to-point fashion, hubs are
`generally used in FC-AL topologies, and can be used in a complementary role to switches
`in fabric topologies. Compared to switches, hubs are lower cost. They are useful to
`simplify cable management and contain bypass control switches that enable failed nodes
`on a loop to be bypassed without compromising the integrity of the loop. The hub’s
`bypass control switches also enable nodes to be hot plugged into a Storage Area Network
`or removed with affecting loop operation.
`
`Figure 5. SAN Interconnected with a FC-AL and Hub
`
`Switches
`
`Switches are used to create Fibre Channel fabrics. They provide the same resiliency
`features as hubs and enable the fabric’s aggregate bandwidth to scale as nodes are
`added. With hub-connected Storage Area Networks, aggregate bandwidth remains
`constant as nodes are added; hence, bandwidth per node decreases as more nodes
`share a fixed amount of bandwidth. With switched fabrics, bandwidth per node remains
`constant as nodes are added and hence, the aggregate bandwidth of the fabric increases
`as nodes are added; aggregate bandwidth is proportional to the number of nodes.
`
`Fabric
`Loop .....
`
`Figure 6. SAN With Switched and Shared (Loop) Interconnects
`
`MYLEX
`
`IBM-Oracle 1006
`Page 9 of 22
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`

`

`Clusters
`
`A cluster is a group of autonomous servers that work together to enhance reliability and
`saleability, and can be managed as a single entity to reduce management costs. Clusters
`always share storage devices and sometimes share data.
`
`Cluster Models
`
`Clusters have been implemented using the Shared Disk and Shared Nothing models:
`
`¯ Shared Disk Model -- Data is simultaneously shared by cluster nodes. An access
`control mechanism, generally referred to as a distributed lock manager, synchronizes
`access from multiple nodes to shared data. Example: Digital VAXClusters.
`¯ Shared Nothing Model - Access to data is shared but at any point in time, disk
`volumes are exclusively owned by one of the nodes. Example: Microsoft NT Clusters
`(NT/E 4.0). In advanced shared nothing clusters, nodes can access data they do not
`own through the node that own the data. Example: Next generation NT Clusters.
`
`Advocates of the Shared Nothing model claim that Shared Nothing clusters are more
`scaleable because the overhead of a distributed lock manager increases as nodes are
`added and eventually bottlenecks the cluster.
`
`Figure 7. Four Node Cluster With Shared Access to RAID Arrays
`
`Clusters Use SAN Technologies
`
`¯ Data is removed from the network and stored on the network behind the servers,
`¯ Storage model is server-independent, not server-dependent,
`¯ Access to storage devices is shared, generally across high performance links,
`¯
`I/O bandwidth is scaleable (with switches); storage capacity is scaleable,
`¯ Redundant links can be used for fault tolerance and higher data availability,
`¯ Data is centralized; security and storage management can be enhanced,
`¯ Storage can be added incrementally; server and storage investments are de-coupled,
`¯ Storage nodes communicate and exchange data (in advanced cluster designs),
`¯ Hubs or switches provide simplified cable management and increased resiliency, and
`¯
`Total cost-of-ownership (TCO) decreases.
`
`MYLEX
`
`IBM-Oracle 1006
`Page 10 of 22
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`

`

`Network-Attached Storage
`
`Network-Attached Storage is implemented with devices directly attach to client networks,
`typically Ethernet LAN’s, and provide optimized file services to clients and servers on the
`network using standard file I/O protocols such as NFS and SMB. Network-Attached
`Storage is essentially a specialized server that functions as a server in a client-server
`relationship with other network computers requesting file access.
`
`~ NAS
`
`Figure 8. NAS on LAN Segments and Connected to SAN
`
`SAN’s and Network-Attached Storage (NAS) are complementary technologies. A NAS
`device functions like a mini-SAN for LAN segments. With NAS devices, storage is moved
`from PC’s and workstations to file access optimized NAS devices where it can be
`protected, secured and managed. NAS design objectives are similar to SAN objectives
`but at lower price points.
`
`¯
`
`¯ Workstation-dependent storage is replaced by workstation-independent storage,
`¯ Data is centralized at the workgroup level where it can be more easily secured,
`shared, RAID-protected, backed-up and accessed in an optimal fashion by all clients,
`LAN’s can be more easily designed to avoid bottlenecks with centralized NAS storage
`on shared or dedicated LAN segments,
`¯ Modular expansion is enabled; workstation and storage investments are de-coupled,
`¯ Redundant links can be used to increase data accessibility, and
`¯
`Total cost-of-ownership (TCO) decreases.
`
`MYLEX
`
`IBM-Oracle 1006
`Page 11 of 22
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`

`

`SAN Connectivity
`
`Fibre Channel Interface -- Fibre Channel is the optimal interface for storage arrays used
`in SAN applications. It provides the performance, distance and scaleability required for
`SAN environments. The Fibre Channel standard is widely supported and a broad range
`of Fibre Channel interconnect devices (hubs and switches) and storage devices (RAID
`arrays, tape and optical libraries, and disk, tape and optical drives) will be available with
`varying levels of features and performance in a competitive market environment.
`
`Dual Channels - High performance SAN-attached storage devices require multiple front-
`end SAN channels for performance and fault tolerance. Dual channel arrays offer twice
`the potential performance of single channel arrays at marginally higher costs and provide
`continuous access to data access if a SAN interconnect device or link fails.
`
`Heterogeneous Host Support
`
`Most enterprises have heterogeneous computing environments with mainframes in the
`data center, and UNIX, NT or NetWare servers distributed across the network.
`Investments in these systems (acquisition, application development and infrastructure
`costs) are substantial and migration to a homogeneous environment is a multi-year
`proposition. SAN-attached RAID arrays should support storage volumes formatted with
`different file systems and allow heteroqeneous systems to access to the volumes.
`
`Data Availability Features
`
`Duplex RAID Controllers - SAN’s should be desiqned without any single point of failure
`that can cause storage devices to become inaccessible. SAN-attached arrays should be
`configured with duplex controllers and with the disks connected to both controllers.
`Multiple SAN interfaces (on each controller) and duplex controllers with shared disks
`provide the level of fault tolerance required in SAN configurations. Redundant paths to
`data is a necessary but not a sufficient condition for high availability.
`
`Transparent Host Independent Failover- In addition to redundancy, controllers should
`implement a transparent failover/failback scheme such that logical disks, i.e. logical arrays,
`are continuously accessible. With a Fibre Channel interconnect, each controller requires a
`port held in reserve to accommodate a controller failover, i.e. assume a failed controller’s
`port ID; although the Fibre Channel standard allows ports to have multiple addresses, this
`feature has not been implemented in Fibre Channel chips. Failover and failback should be
`implemented such that transitions occur without any required host intervention.
`
`Alternate Path Support -- Following the no single point of failure principle, SAN-attached
`servers should have redundant Host Bus Adapters (HBA’s) with alternate path software
`support. Alternate path is generally implemented as a software driver and provides a level
`of indirection between the OS and HBA’s. If one HBA fails, the driver redirects I/O’s
`intended for the failed HBA to the alternate HBA so that I/O requests can be satisfied
`without the host OS’s knowing that an alternate path to storage was used.
`
`MYLEX 11
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`

`Data Integrity Features
`
`Mirrored Write Caching -- Most external RAID controllers implement write-back caching
`to enhance performance but few implement a mirrored write-back caching scheme to
`protect data. Data in a controller’s cache is vulnerable to power loss or controller failures
`until it is written to disk. To make matters far worse, if data in a write-back cache is lost,
`the application is oblivious to the loss since the controller has already acknowledged the
`write as complete. Controller battery back-up units can hold-up cache contents during
`power outages but cannot move cached data to an operational controller which can write it
`to disk. Mirroring write-back caches across controllers solves this problem and can be
`designed with minimal effect on cost or performance. With a mirrored cache architecture,
`I/O’s are written to cache memories in multiple controllers before the write is
`acknowledged as complete. If one controller subsequently fails, the surviving controller
`flushes the contents of the failed controller’s cache (which are stored in its cache) safely to
`disk. Mirrored caches protect data like mirrored disks.
`
`Data Management Features
`
`SAN-attached RAID arrays should support disk mirroring, all the commonly used RAID
`levels, on-line expansion of logical drives, on-line addition of logical drives and other data
`management software. Network-wide array management should be available from any
`client machine on the network.
`
`Bandwidth Scaling Capabilities
`
`Scaleable I/O Performance - SAN’s require a balanced design. The number (and
`compute power) of servers attached to a SAN can vary by orders of magnitudes, and
`SAN’s naturally tend to expand over time. However, adding servers to a SAN will result in
`marginal performance gains if the SAN-attached RAID arrays lack the horsepower to feed
`the additional nodes. Scaleable compute power requires scaleable I/O power. External
`storage arrays inherently provide scaleable I/O performance since arrays can be
`incrementally added to a SAN. However, a large number of under-powered or disk
`channel limited arrays are less cost-effective and more difficult to manage than a smaller
`number of arrays with performance better matched to the SAN’s I/O requirements.
`
`Active-Active Operation -- Duplex controllers can operate in active-passive or active-
`active mode just like cluster nodes. In this context, active-active implies a duplex controller
`configuration with both controllers simultaneously servicing SAN I/O requests. This is
`analogous to the active-active operation of cluster nodes. To realize the full performance
`potential and total cost-of-ownership (TCO) effectiveness of a SAN, all storage resources,
`must contribute to performance. Controllers that operate in active-passive mode with one
`controller idle until the other fails is a waste of a valuable SAN resource.
`
`MYLEX 12
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`

`Capacity Scaling Capabilities
`
`Scaleable I/O Capacity -- System storage has been increasing 50% a year since the first
`disk drive was invented. SAN’s require controllers with surplus back-end channel capacity
`to accommodate expanding storage needs. Storage controllers that only support a few
`disk channels are marginal for SAN applications. Controllers with more back-end
`channels can not only accommodate more storage but their arrays can also be configured
`to provide performance and data availability benefits. Logical arrays on controllers with
`two or three disk channels are striped vertically down a channel. Since applications direct
`most I/O to a single logical array, vertically stripping arrays can cause a single I/0
`processor (lOP) to become a bottleneck (the hot disk phenomena moved into the
`controller). Horizontal striping balances the I/O load across IOP’s.
`
`lOP
`
`External RAID Controller
`lOP
`lOP
`lOP
`
`lOP
`
`Figure 9. Vertically and horizontally stripped arrays.
`
`If an lOP fails, vertically striped arrays on the failed channel become unavailable to the
`controller with the failed lOP. However, if a RAID 5 array is horizontally striped across
`channels, then an lOP failure causes the loss of a single disk which RAID 5 algorithms
`can repair on-the-fly without disrupting application access to data. This failure mode is
`identical to a single disk failure in a RAID 5 set.
`
`MYLEX
`
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`

`

`Mylex Fibre Channel Product Line
`
`Mylex offers a seamless product line of external RAID array controllers designed to meet
`the performance, connectivity, cost, interface, topology, data integrity, data availability and
`data management requirements of SAN and cluster environments.
`
`Mylex external controllers are ready to be packaged in stand-alone or rack-mountable
`JBOD (disk) enclosures. External controllers are shared storage resources packaged
`apart from systems (internal controllers plug into a system bus, typically PCl).
`
`The RAID firmware and management software implemented across the product line
`deliver a uniform set of data protection and performance optimization features:
`
`¯ At va~ing levels of performance and storage connectivity,
`¯ With dual fibre host interfaces, and Ultra or Ultra-2 LVD disk interfaces, and
`¯ At price points for enW level SAN’s and with performance for enterprise SAN’s.
`
`Mylex array controllers are available in simplex configurations for network servers and
`duplex (dual) configurations for SAN’s and clusters. In duplex mode, advanced features
`are implemented to accelerate performance, protect data and guarantee data accessibility.
`
`¯ Active-active controller operation for increased performance,
`¯
`Transparent failover/failback for high data availability, and
`¯ Cache mirroring for guaranteed data integrity.
`
`Figure 10. Relative Performance
`
`Figure 11. Product Line Features
`
`Duplex controllers (gray boxes) deliver up to twice the performance of simplex controllers
`(white boxes). Fibre controllers provide over twice the performance of SCSl controllers.
`Data protection, accessibility and management features are important in any SAN or
`cluster environment and are uniformly implemented across the product line:
`
`¯ DAC SX
`¯ DAC SF
`¯ DAC FL
`
`Dual Ultra SCSI host ports and four Ultra SCSI disk channels
`Dual Fibre Channel host ports and six Ultra SCSl disk channels
`Dual Fibre Channels host ports and four Ultra-2 LVD disk channels
`
`MYLEX
`
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`

`Heterogeneous Server Support
`Mylex external array controllers can accommodate SAN’s configured with heterogeneous
`operating systems, such as UNIX and NT. Disk volumes are configured into logical arrays
`and then formatted with NTFS or UNIX file systems. Up to eight logical arrays accessed
`as LUN’s (Logical Unit Numbers) can be configured on each controller. With Mylex
`controllers, a logical array is the unit of space allocation and RAID level protection. Each
`logical array can be configured with the RAID level that provide the optimal level of
`performance and fault tolerance for applications accessing the arrays.
`
`NT and UNIX servers can simultaneously access Mylex array controllers formatted with
`NT and UNIX volumes. This level of flexibility is required by enterprise SAN’s and
`facilitates migration from heterogeneous to homogeneous computing environments.
`
`UNIX ~
`System
`
`_ ~ ~] ~ NT
`Server
`~;-A~~
`
`FL Cc 1troller
`
`FL Con oiler
`
`FL Controller
`
`II
`
`||
`
`FL Controller
`
`I
`
`Figure 12. DAC FL Attahed to a Fibre Channel SAN
`
`In Figure 12, two pairs of duplex DAC FL controllers are SAN-attached. Each controller
`has redundant paths to host systems and pairs of controllers provide redundant paths to
`disks. The dark shaded disks are formatted with UNIX file systems and the lightly shaded
`disks with NTFS files systems. The SAN-attached servers can have multiple paths
`through the SAN interconnect to both pairs of redundant controllers, and redundant paths
`from the controllers to the disks are provided for fault tolerance and high data availability.
`
`Mylex SAN-attached controllers provide reliable and simultaneous access from
`heterogeneous servers to provide a higher level of resource sharing and an integrated
`storage environment.
`
`MYLEX
`
`is
`
`IBM-Oracle 1006
`Page 16 of 22
`
`

`

`Active-Active with Transparent Failover / Failback
`
`A key SAN benefit is high data availability; SAN devices should be able to fail without
`negatively impacting access to data (aside from momentary transition delays). Mylex
`external RAID array controllers incorporate features that increase data accessibility.
`
`¯ Active-Active Controller O