Transcript
SANworks by Compaq Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link Part Number: EK-DRMWD-AA. E01
Fifth Edition (May 2002) Product Version:
ACS Version 8.6-4P
This document describes extended wavelength division multiplexing (WDM) configurations and products that are available for use with the SANworksTM Data Replication Manager by Compaq. The Data Replication Manager disaster-tolerant solution provides controller-based mirroring across an extended Fibre Channel intersite link that can be enhanced by the additional benefits of WDM.
For the latest version of these application notes and other DRM documentation, visit the Compaq storage website at: http://www.compaq.com/products/sanworks/drm/index.html.
b
© 2002 Compaq Information Technologies Group, L.P. Compaq, the Compaq logo, SANworks, and StorageWorks are trademarks of Compaq Information Technologies Group, L.P. in the U.S. and/or other countries. Microsoft and Windows are trademarks of the Microsoft Corporation in the U.S. and/or other countries. All other product names mentioned herein may be trademarks of their respective companies. Confidential computer software. Valid license from Compaq required for possession, use or copying. Consistent with FAR 12.211 and 12.212, Commercial Computer Software, Computer Software Documentation, and Technical Data for Commercial Items are licensed to the U.S. Government under vendor's standard commercial license. Compaq shall not be liable for technical or editorial errors or omissions contained herein. The information is provided “as is” without warranty of any kind and is subject to change without notice. The warranties for Compaq products are set forth in the express limited warranty statements accompanying such products. Nothing herein should be construed as constituting an additional warranty. Compaq service tool software, including associated documentation, is the property of and contains confidential technology of Compaq Computer Corporation or its affiliates. Service customer is hereby licensed to use the software only for activities directly relating to the delivery of, and only during the term of, the applicable services delivered by Compaq or its authorized service provider. Customer may not modify or reverse engineer, remove, or transfer the software or make the software or any resultant diagnosis or system management data available to other parties without Compaq’s or its authorized service provider’s consent. Upon termination of the services, customer will, at Compaq’s or its service provider’s option, destroy or return the software and associated documentation in its possession. Printed in the U.S.A. Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link Fifth Edition (May 2002) Part Number: EK-DRMWD-AA. E01
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Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
Application Notes Contents
Application Notes Contents These Application Notes cover the following major topics: •
About This Document, page 4
•
Qualified Vendor Products for WDM, page 5
•
Warranty Information, page 5
•
Data Replication Manager Overview, page 5
•
Wavelength Division Multiplexing Overview, page 6
•
Configuration, page 9
•
Performance, page 12
•
Glossary, page 15
Intended Audience This document is intended for customers using a SANworks Data Replication Manager by Compaq solution and who are interested in running Data Replication Manager (DRM) over a wavelength division multiplexing (WDM)-enabled intersite link.
Related Documentation Table 1 lists documentation that may prove helpful with the discussion of DRM, WDM, and HSG80 array controller software. Additional documentation, including white papers and best practices documents, is available via the Compaq website at: http://www.compaq.com/products/sanworks/drm/index.html. Table 1: Related Documentation Document Title
Part Number
SANworks by Compaq Data Replication Manager HSG80 ACS Version 8.6-4P Configuration Guide
AA-RPHZD-TE
SANworks by Compaq Data Replication Manager HSG80 ACS Version 8.6-4P Failover/Failback Guide
AA-RPJ0C-TE
SANworks by Compaq Data Replication Manager HSG80 ACS Version 8.6-4P Release Notes
AA-RPJ2C-TE
Compaq StorageWorks HSG80 Array Controller ACS Version 8.6 CLI Reference Guide
EK-G80CL-RA. A01
Compaq StorageWorks HSG80 Array Controller ACS Version 8.6 Troubleshooting Reference Guide
EK-G80TR-SA. A01
SANworks by Compaq HSG80 ACS Version 8.6-4P Data Replication Manager Design Guide Application Notes
AA-RQ78A-TE
Compaq StorageWorks Heterogeneous OpenSAN Design Reference Guide
AA-RMPNA-TE
Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
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Compaq Technical Support
Compaq Technical Support In North America, call the Compaq Technical Phone Support Center at 1-800-OK-COMPAQ. This service is available 24 hours a day, 7 days a week. Be sure to have the following information available before you call Compaq: •
Technical support registration number (if applicable)
•
Product serial numbers
•
Product model names and numbers
•
Applicable error messages
•
Operating system type and revision level
•
Detailed, specific questions
Outside North America, call the nearest Compaq Technical Support Phone Center. Telephone numbers for world wide Technical Support Centers are listed on the Compaq website at www.compaq.com.
Compaq Website Check the Compaq website for more information on the complete line of Fibre Channel storage products, product certification, technical information, updates, and documentation. This information is accessed through the Compaq website at: http://www.compaq.com/storage
Compaq Authorized Reseller Consultation on all aspects of networking from purchasing to setup and network management is available through your Compaq Authorized Reseller. For the name of your nearest Compaq Authorized Reseller: •
In the United States, call 1-800-345-1518.
•
In Canada, call 1-800-263-5868.
•
Elsewhere, see the Compaq website for locations and telephone numbers.
About This Document This document provides a brief introduction to WDM technology with DRM, and lists the third-party vendor products that are qualified by Compaq to provide a WDM interface over a Fibre Channel intersite link (ISL) in the DRM environment.
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Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
Qualified Vendor Products for WDM
Qualified Vendor Products for WDM The vendor products listed in Table 2 are qualified for use as WDM devices in a DRM solution. The vendors are listed in alphabetical order. Compaq does not rate the devices or make recommendations about these vendors. Users should make their own vendor product evaluations. This document will be revised as additional vendor products are qualified. Table 2: DRM Vendor Qualified WDM Devices
Vendor Name
Model
Compaq Tested Distance (km)
Channels
Vendor Information and Product Specifications
ADVA
FSP II
32/64*
100
http://www.advaoptical.com
Cisco
ONS 15540
32
30
http://www.cisco.com
Controlware
Wavepilot
8,16, or 32
50
http://www.controlware.com
CNT
UltraNet Wave Multiplexer
64
50
http://www.cnt.com
Fujitsu
Flashwave 320 G
32
100
http://www.fnc.fujitsu.com
LuxN
WaveStation
16 or 32
100
http://www.luxn.com
LuxN
Wavfarer WS 3217
8
72.2
http://www.luxn.com
Nortel
Optera Metro
32/64*
100
http://www.nortelnetworks.com
ONI
Online 9000
33/66*
100
http://www.oni.com
PhotoniXnet
LightEdge LE701
4
50
http://www.photonixnet.com/english/
* protected/unprotected
For a list of all the operating systems supported with WDM in a DRM environment, visit the following website: http://www.compaq.com/products/sanworks/drm/index.html Select the Software Support Matrices link, then choose a particular operating system to obtain its minimum requirements.
Warranty Information Compaq does not warrant third-party products. Please consult the original equipment manufacturer for warranty information.
Data Replication Manager Overview DRM is a storage-based disk mirroring and workload migration solution that copies data online and in real time to remote locations through an extended storage area network (SAN). During normal data processing, data is written to local and remote sites. Although copies of data reside at both sites, host data access normally occurs through the local site unless a failure or catastrophe occurs that disables processing at that site. When such a failure occurs, the remote site can continue processing data.
Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
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Wavelength Division Multiplexing Overview
DRM provides rapid data access recovery and continued data processing after the loss of one or more components. DRM uses the peer-to-peer remote copy function of the HSG80 controller to achieve data replication. HSG80 controller pairs at the local site are connected to their partner HSG80 controller pairs at the remote site. Figure 1 illustrates a DRM setup using single mode very long distance Gigabit Interface Converters (GBICs) for the long-distance link. Network Interconnect Host
Host
Switch Y
~ ~
Switch A
Very Long Distance GBIC
Up to 100 km 9 micron single-mode fiber
Controller A
Switch B
Switch Z
~ ~
Normal GBIC
Controller Y
Up to 100 km 9 micron single-mode fiber CXO7162B
Figure 1: Data Replication Manager (typical configuration without WDM)
Wavelength Division Multiplexing Overview Wavelength division multiplexing is an optical technology used to add connection capacity over an existing fiber optic network. It works by combining and transmitting multiple optical signals simultaneously at different wavelengths down a single fiber. In effect, one fiber is transformed into multiple virtual fibers. This allows WDM to multiply the effective bandwidth capacity of the optical fiber. For example, by multiplexing eight 1-Gb/s signals into a single fiber, the data-carrying capacity of that fiber increases from 1 Gb/s to 8 Gb/s in aggregate. Single fibers are currently able to transmit data at speeds up to 400 Gb/s. Research is progressing toward adding more and more channels to a single fiber, increasing capacity accordingly. The maximum data-carrying capacity that can be designed into a WDM system is strongly dependent on the spacing between the wavelengths being used. For silica fiber, the range of usable wavelengths lies within two spectral windows, nominally centered around 1300 and 1550 nm and approximately 30-nm wide.
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Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
Wavelength Division Multiplexing Overview
The spectral windows occur within the infrared spectrum where the optical scattering and absorption losses associated with silica fiber are minimal and transmission is maximized. Fiber optic systems in general are currently designed to operate within these two transmission windows. WDM systems typically combine multiple channels within either window where channel separations are on the order of the window width divided by the number of channels. The following is an example: (30 nm window width) / (8 channels) = 3.75 nm channel spacing
Thus, the effects of upgrading a WDM system to provide more channels are: •
Decreased spacing (and the optical isolation) between adjacent channels
•
Increased potential for channel-to-channel crosstalk
The most demanding of WDM configurations combine up to 128 channels within a single transmission window and are known as dense-WDM (DWDM) systems. Adjacent wavelengths in DWDM systems are separated by distances of less than 1.6 nm. Configurations with adjacent wavelengths greater than 1.6 nm are known as coarse-WDM (CWDM) systems. A key advantage to WDM is that most architectures are protocol and bit-rate independent. WDM-based networks can simultaneously transmit data in Fibre Channel, Internet Protocol (IP), Asynchronous Transfer Mode (ATM), Synchronous Optical Network (SONET)/Synchronous Digital Hierarchy (SDH), and Ethernet protocols, and can simultaneously handle multiple bit rates.
Commercial Applications From a Quality of Service (QoS) viewpoint, WDM-based networks create a lower-cost way to quickly respond to customers’ bandwidth demands and protocol changes. This is because each new wavelength is a new, full bandwidth communications pipe. In many areas of the world it is much cheaper to deploy WDM technology on existing fiber than it is to pull a new fiber. Once WDM has been implemented, service providers can establish a grow-as-you-go infrastructure. WDM gives service providers the flexibility to expand capacity in any portion of their networks—an advantage no other technology can offer. Carriers can address specific problem areas that are congested because of high capacity demands. This is especially helpful where multiple rings intersect between two nodes, resulting in fiber exhaust. (Fiber “exhaust” means that the traffic volume on the Internet and other networks have exhausted collective bandwidth available through installed optical fiber lines.) By partitioning and maintaining different dedicated wavelengths for different customers, service providers, for example, can lease individual wavelengths—as opposed to an entire fiber—to their high-use business customers.
WDM Product Variations WDM vendors currently offer at least four variations of the products described in these application notes. These variations are significant and warrant a separate discussion because of their potential for compatibility issues with DRM systems. WDM system architectures can be delineated in the most general sense as being: •
Passive (optically and with respect to transmission protocol)
•
Active with respect to signal amplification
•
Active with respect to protocol handling
•
Data Path Protection
Most WDM products on the market today fit uniquely into one of these categories, or have been designed to combine attributes of each.
Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
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Wavelength Division Multiplexing Overview
Passive Systems These WDM systems are transparent to transmission protocol and data rate. As such, they establish open interfaces that give operators the flexibility to provide Fibre Channel, SONET/SDH, asynchronous/Plesiochronous Digital Hierarchy (PDH), ATM, Frame Relay, and other protocols over the same fiber. A truly passive optical system also passes the optical signal without any form of signal conditioning such as amplification or attenuation (beyond the levels inherent to the system components).
Active Signal Amplification Certain WDM products are offered with line amplifiers and attenuators. These features are included primarily to facilitate interfacing via fiber optic links to other telecom hardware. Line amplifiers allow the boosting of weak signals received from peripheral network components, as well as boosting the signals being transmitted that might otherwise fall below the threshold sensitivities of receiving equipment. Similarly, incoming and outgoing signals can be attenuated if they are sensed as being above receiver saturation levels. These active systems typically monitor power levels to ensure operation is maintained within the power budget of the hardware. Power monitoring capability is usually accomplished with hardware/software control loops, which can add significantly to the cost of the product.
Active Protocol Handling While most WDM systems are designed to be protocol independent, products are available that offer a system with protocol specific capabilities for Fibre Channel. This design enables digital time division multiplexing (TDM) on top of existing optical multiplexing to support multiple channels per wavelength. This design also allows for network monitoring, digital re-timing (to reduce jitter), link integrity monitoring, and distance buffering. At the time of the publication of this application note, this architecture was available for supporting a mix of Fibre Channel or gigabit Ethernet protocols only. Considering the added sensitivity to protocols, this WDM variant seems straightforward in point-to-point configurations, but may require additional and potentially costly transmission hardware when deployed in meshed networks.
Data Path Protection Most WDM systems can be configured to provide protection against loss of service. Path switching and equipment switching are offered by most WDM vendors to provide protection of data traffic from fiber cuts and equipment failures: •
Path switching protects the signal carried between the local and remote WDM hardware site locations.
•
Equipment switching protects equipment that is not otherwise protected by path switching.
The idea of data path protection is to provide an appropriate failover mechanism that automatically transfers functionality from one circuit to another. The price the user pays for this protection feature is connection capacity. One protected data path requires two identical end-to-end connections (two complete data channels). For example, a 16-channel WDM system provides either 16 unprotected data channels, or a maximum of 8 protected channels.
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Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
Configuration
System Characteristics Acceptable and optimal WDM systems have certain key characteristics. These characteristics are recommended for any WDM system in order for carriers to realize the full potential of this technology. The following characteristics are desired in a WDM system: •
Uses the full capacity of the customers’ existing dark fiber.
•
Offers component reliability, 24x7 availability, and expandability.
•
Provides optical signal amplification and attenuation. This is desirable on the client side and long-haul side interfaces to increase the transmitted/received signal-to-noise ratio.
•
Provides signal conditioning (that is, the retiming and reshaping of the optical data-carrying signal) for optimization of the bit error rate.
•
Offers channel add/drop capability (the ability to change the number of data channels by adding or dropping optical wavelengths at any network node location).
•
Allows compensation of power levels (preferably automatic or without manual intervention), especially to facilitate adding (or dropping) channels.
•
Provides upgradable channel capacity and/or bit rate. Each time the number of channels or the bit rate is doubled, 3 dB of additional signal-to-noise margin is needed.
•
Allows inter-operability with DRM, which requires standards-compliant interfaces such as Fibre Channel, SONET, ATM, and so on.
Configuration The following configuration issues are defined and described in the following sections: •
Test Configuration: DRM over WDM
•
Interfaces
Test Configuration: DRM over WDM The configurations addressed in these application notes and pictured in Figure 2 can be described as a disaster-tolerant data storage solution operating over extended WDM-enabled intersite links. The components of this DRM solution being tested consist of: •
Four HSG80 Array Controllers running ACS Version 8.XP
•
Four Compaq Fibre Channel SAN switches
•
Microsoft Windows 2000
•
A pair of WDM boxes under test
The HSG80 Array Controllers running ACS Version 8.XP, along with Compaq switches, provide a DRM solution for distributed environments. With an array controller connected to a host at a primary data center, configurations can be created with local critical data replicated to remote storage sites.
Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
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Configuration
Initiator site
Target site
Switch A
Switch Y
WDM
Link redundancy: non-existent Cost: low
WDM
ISL failure risk: high Switch B
Switch Z CXO7205A
Figure 2a. Simple point-to-point configuration using one long-haul fiber link
Initiator site
Target site
Switch A
Switch Y
Link redundancy: duality Cost: low-medium
WDM
WDM
Switch B
Risk: medium Switch Z CXO7206B
Figure 2b. Point-to-point loop configuration using two long-haul fiber links Target site
Initiator site Switch A
Link redundancy: fully redundant
Switch Y WDM
WDM
Cost: high WDM
Risk: lowest
WDM
Switch B
Switch Z CXO7207A
Figure 2c. Redundant WDM loop configuration using two (or more) long-haul fiber links Figure 2: Comparison of three intersite link options
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Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
Configuration
The addition of WDM hardware allows for multiplexing of multiple optical signals that can be amplified as a group and transmitted long distances over a single fiber. The configurations shown in Figure 2 have the WDM hardware integrated into the intersite link and are configured to simultaneously support four optical signals: •
Send and receive for fabric 1
•
Send and receive for fabric 2
The four signals are optically multiplexed and transmitted down the duplex fiber to link the primary and remote data centers. The performance of this configuration was certified by imposing a requirement to demonstrate disaster-tolerant operation over a series of tests that simulated possible failure scenarios specific to the WDM-enabled intersite links. When designing the desired DRM solution for a given application, another key consideration is the intersite link that is used to connect the local and remote storage sites. A trade-off exists between the higher cost of providing redundant links (to lower the risk of intersite link failure) and the cost reduction associated with a simpler system having a single point of failure. Figure 2 represents a comparison of three possibilities for DRM systems. As one would expect, a single fiber link (Figure 2a) offers a lower cost solution for applications that can tolerate periods of downtime. Figure 2b shows a configuration that provides link redundancy, with medium risk, and increased cost. The configuration in Figure 2c is diverse routed to provide WDM redundancy, which is recommended for applications requiring high availability.
Interfaces The physical interfaces that connect the DRM system to the WDM-enabled intersite link are straightforward: there are two duplex fiber optic cables that make up the fabric links between the optical switches of each DRM site and the input modules to the WDM hardware (see Figure 3). Each Fibre Channel switch contains multiple I/O ports with GBICs. The switch has the function of relaying or routing incoming signals from one switch port to another. The GBIC interface serves as an optical transceiver that provides high-speed serial links by: •
Conversion of incoming optical signals from the fiber optic link to equivalent electrical signals for the switch.
•
Conversion of electrical signals from the switch to optical signals that are to be launched down the fiber.
The specifications of the GBIC-to-fiber interface conform to the American National Standards Institute’s (ANSI) Fibre Channel, FC-0 Standard for long wavelength operation.1 The interface at the WDM hardware similarly converts the incoming optical signals to electrical signals, then uses each signal to modulate a narrowband laser. The resulting optical signal is then multiplexed with other such signals before being launched over the long-haul fiber link. As before, the fiber-to-WDM hardware interface must support the ANSI Fibre Channel, FC-0 Standard.
1.
American National Standards Institute Inc. (ANSI), T11, Fibre Channel-Physical and Signaling Interface (100-SM-LC-L, rev. 3.0).
Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
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Performance
Network Interconnect Host
Host
Switch A
WDM
~ ~
Wavelength division MUX/DEMUX hardware
Switch Y
WDM
Intersite link
Controller A
Controller Y
Switch Z WDM
~ ~
Switch B WDM
Intersite link CXO7197B
Figure 3: Data Replication Manager configured with a WDM-enabled intersite link
Performance This section describes the following performance issues: •
Data Rates
•
Extended Fabric
•
Latency
Data Rates The tests to determine data rates were simplistic, performed in a non-DRM environment, and were only designed to illustrate performance over distance for varying fiber lengths. As such, 128 block (64 KB) write operations were issued to multiple units over very restricted seek distances. This resulted in all data being written to cache (eliminating disk accesses). The restricted seek range prevented performance degradation due to cache locking, and the multiple units allowed several I/O operations to be in process at the same time. Testing was performed at intersite link distances of 25, 50, 75, and 100 km. The extended fabric feature was enabled with:
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•
27 buffer-to-buffer (bb) credits at the 25 km and 50 km links
•
55 bb credits for the 75 km and 100 km links
Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
Performance
Figure 4 shows the performance results for distances out to 100 km for buffer-to-buffer credit settings of 8, 27, and 55. FC THROUGHPUT VS. BB CREDITS
THROUGHPUT (MB/S)
120 100 80 8 bb credits 60
27 bb credits 55 bb credits
40 20 0 0
25
50
75
100
DISTANCE (KM)
Figure 4: Fibre Channel performance over distance
Extended Fabric Fibre Channel fabrics are made up of one or more electro-optical switches connected to each other with fiber optic cables. These fabric lengths are capable of being extended long distances (up to approximately 100 km) without the need for protocol translation, while maintaining efficient link utilization. To extend a Fibre Channel fabric, it is necessary to account for the time it takes a single Fibre Channel data frame to travel the round trip distance over the fiber optic link. If the expansion ports (E_ports) on all the switches have one E_port buffer (or buffer-to-buffer credit), then only a single frame can be sent over the fabric link at a time. For long distances, sending one frame at a time is very inefficient. It makes more sense to send frames end-to-end and in succession, at a rate that “fills up” the fiber link with Fibre Channel frames. To “fill up” a fiber link, calculate the number of frames that can exist end-to-end on the fiber link at a time. Since frames are made up of a fixed number of bytes, it is a simple exercise to determine the number of bytes that can exist on a round-trip loop at one time for a given data rate. As an example, consider data flowing at a rate of 100 MB/s down a 10-km fiber. Since a pulse of light travels down fiber at a speed of 5 microseconds per kilometer, the round-trip travel time for a single pulse can be calculated as: 2 x (10 km x 5 microseconds/km) = 100 microseconds
In 100 microseconds, the number of bytes that can fill up the round trip distance is: 100 microseconds x 100 MB/second = 10000 bytes
Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
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Performance
To determine the number of frames that will fill up this same round-trip distance, divide the total number of bytes by the frame size. For a frame size of 2 KB/frame, the calculation yields: 10000 bytes / (2000 bytes per frame) = 5
Thus, to be able to efficiently fill up the round-trip fiber distance (20 km) with 2-KB data frames at a transmission rate of 100 MB/s, the E_port would need to be configured with at least 5 buffer-to-buffer credits. Similar calculations using 2-KB frames would yield 25 credits for 50 km and 50 credits for 100 km. The factory configuration for the Compaq 8- and 16-port switches (including the integrated SAN switches) currently provides for 16 buffer-to-buffer credits per E_port. These credits cannot be adjusted unless licenses are purchased and installed to enable the Extended Fabric feature. This license is available beginning with version 2.6 of the 8- and 16-port switch firmware. Once enabled, Extended Fabric allows the user to increase the number of E_port credits to either 27 or 60. These settings will then allow the maximum data transmission rate to be maintained over distances of up to 100 km.
Latency Latency tests were performed to isolate the effects of the WDM hardware on the total round-trip transport time. The results were obtained in the following manner: •
Measurement of the total round-trip transport time across the WDM-enabled long haul link.
•
Measurement of the total round-trip transport time across the same long haul link without (bypassing) the WDM hardware.
•
Determination of the WDM-induced latency was obtained by subtracting the two measurements.
The results that can be solely attributed to the WDM components yielded total round-trip delay on the order of 1 microsecond. Since there are four WDM “boxes” encountered during one round trip, the delay from a single box is on the order of 0.25 microseconds, which is considered negligible with respect to any effects on DRM functionality.
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Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
Glossary
Glossary This glossary defines terms relevant to the Data Replication Manager and a WDM link. array controller
See controller.
asynchronous mode
A mode of operation of the remote copy set where the write operation reports command completion to the host after the data is on the initiating controller, but before completion of the remote command. See also synchronous mode.
Asynchronous Transfer Mode (ATM)
A dedicated connection switching technology that organizes digital data into 53-byte cell units and transmits them over a physical medium using digital signal technology. ATM is capable of transmitting at speeds of 155 or 622 MBps and faster.
buffer-to-buffer (bb) credit
A link-level flow control mechanism. Buffers in the expansion port of switches used to determine how many frames can be outstanding when sent to a recipient.
controller
A hardware device that uses software to facilitate communications between a host and one or more storage devices organized in an array. The HS-series StorageWorksTM family of controllers are all array controllers.
coarse wavelength division multiplexing (CWDM)
Transmitting multiple spaced wavelengths through the same fiber. Wavelengths are spaced greater than 1.6 nanometers apart.
dark fiber
Unused fiber optic cable.
data rate
The amount of data transferred per second by a communications channel, computing device, or storage device.
default gateway
The default path that a computer or router uses to forward and route data between two or more networks that have different protocols.
dense wavelength division multiplexing (DWDM)
Transmitting multiple closely spaced wavelengths through the same fiber. This often means wavelength spacings of 1.6 nanometers or less apart.
dual-redundant configuration
A storage subsystem configuration that consists of two active controllers operating as a single controller. If one controller fails, the other assumes control of the failing controller’s devices.
fabric
A network of one or more Fibre Channel switches.
Fibre Channel (FC)
A technology protocol standardized by ANSI that allows very high-speed, switching-based serial transmissions.
Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
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Glossary
Fibre Channel switch
A device that provides high-speed, high-bandwidth routing of data (in Fibre Channel protocol) via link-level addressing.
frame
The basic unit of communication using the Fibre Channel protocol. Each frame consists of a payload encapsulated in control information. The maximum size of the payload is 2112 bytes.
Gigabit Interface Converter (GBIC)
Serial electrical-to-serial optical transceiver modules. GBIC devices are available for short-range, long-range, and very long distances. •
Short range: MMF, 850 nm
•
Long range: SMF, 1310 nm
•
Very long distance: SMF, 1550 nm
The fiber mode of the GBIC at the switch matches the input to the WDM device. For example, if the GBIC at the switch is SMF, then the input to the WDM device is SMF.
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Internet Protocol (IP)
An address of a device on a network using TCP/IP.
intersite link (ISL)
A connection between two switches using their expansion ports.
latency
The amount of time required for a transmission to reach its destination.
link
A connection between two adjacent Fibre Channel ports, consisting of a transmit fiber and a receive fiber. An example is the connection between the Fibre Channel switch port and the HSG80 controller.
local site
For subsystems using the disaster tolerant Data Replication Manager solution, the local site is the SAN that is the primary source of information. When a system outage occurs, the database is recovered from the remote site SAN.
mirroring
The act of creating an exact copy or image of data.
multimode fiber (MMF)
Optical fiber that is designed to carry multiple short wavelength light rays or modes concurrently. For ranges of 0.5 to 500 meters, 50-micron fiber is used. For ranges of 0.5 to 300 meters, 62.5-micron fiber is used. These ranges are shorter at 2 Gb speeds.
network
In data communication, a configuration in which two or more terminals or devices are connected to enable information transfer.
Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
Glossary
plesiochronous
Refers to a transmission where the sending and receiving devices are synchronized, but set to different clocks. Although the bits may not arrive in the same time slot as they were sent, as long as they arrive within a certain defined range, the transmission is said to be plesiochronous.
Plesiochronous Digital Hierarchy (PDH)
A transmission system for voice communication using plesiochronous synchronization.
Quality of Service (QoS)
Each virtual connection in an ATM network has a service category. The performance of the connection is measured by six established QoS parameters, which are outlined by the ATM forum.
redundancy
Using backup components to ensure uninterrupted operation of a system in case of failure.
remote copy set
A Data Replication Manager feature that allows data to be copied (mirrored) from an originating site to a remote site.
remote site
For subsystems using the disaster-tolerant Data Replication Manager, data processing occurs at a local SAN site and the data is replicated or mirrored to the remote site SAN. When local system outage occurs, the database is recovered from the remote site system.
single-mode fiber (SMF)
Optical fiber that is designed for the transmission of a single, long wavelength, ray or mode of light. This 9-micron fiber is used for long distance optical signal transmission. Depending on the GBIC, the range is 2 m to 10 km or 2 m to 100 km.
speed of light through fiber
Approximately 200,000 kilometers per second or 5 microseconds to traverse one kilometer.
subnet mask
Also known as address mask. An IP network that can be reached through a single IP address. All the members of the subnet share the mask value. Members of the subnet can then be referenced more easily. A subnetwork is a network that is part of another network, connected through a gateway, bridge, or router.
Synchronous Digital Hierarchy (SDH)
An international digital telecommunications network hierarchy which standardizes transmission around the bit rate of 51.84 megabits per second, which is also called STS-1. SDH is the European counterpart to SONET.
Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
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Glossary
synchronous mode
A mode of operation of the remote copy set where the data is written simultaneously to the cache of the local subsystem and the cache of the remote subsystem. The I/O completion status is returned to the sender once the I/O is in the cache at both sites. See also asynchronous mode.
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SynchronousOptical Network (SONET)
A broadband networking standard (ANSI T1.105) based on point-to-point optical fibre networks. SONET is the American version of SDH.
time division multiplexing (TDM)
A technology that combines several slow speed transmission channels into one high speed transmission channel. Each low speed channel is located in a time slot.
topology
An interconnection scheme that allows multiple Fibre Channel ports to communicate. For example, point-to-point, arbitrated loop, and switched fabric are all Fibre Channel topologies.
Transmission Control Protocol over Internet Protocol (TCP/IP)
A language governing communications among all computers on the Internet.
wavelength
The distance an electromagnetic wave travels in the time it takes to oscillate through a complete cycle. Wavelengths of light are measured in nanometers (10-9 m) or micrometers (10-6 m).
wavelength division multiplexing (WDM)
A technology that uses multiple lasers to transmit several wavelengths of light simultaneously over a single optical fiber.
Application Notes – Data Replication Manager Over a WDM-enabled Intersite Link
