Hp StorageWorks Data Replication Manager Intersite Link Performance Analyzer

Application Notes

hp StorageWorks

Data Replication Manager Intersite Link

Performance Analyzer

Product Version: ACS Version 8.7P

First Edition (March 2004)

Part Number: AA-RV26A-TE

This document provides instructions for the use of an intersite link performance analyzer tool developed by HP using Microsoft Replication Manager environment.

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® Excel. This tool will help you determine the worst-case I/O impact over distance in a Data

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Data Replication Manager Intersite Link Performance Analyzer Application Notes First Edition (March 2004) Part Number: AA-RV26A-TE

2 Data Replication Manager Intersite Link Performance Analyzer Application Notes

About This Document

These application notes cover the following topics:

■ Data Replication Manager Performance Estimation, page 4

— DRM Link Variables, page 4 — DRM I/O Basic Information, page 5 — Additional Considerations With Asynchronous Transfer Mode, page 5

■ Link Performance Analyzer, page 6

— Tool Inputs, page 6 — Tool Results, page 6 — Simplifying Assumptions, page 7 — Final Considerations, page 7

■ Performance Analyzer Examples, page 8

Intended Audience

This document is intended for customers who are using Data Replication Manager (DRM) and need to estimate the effects of distance on applications that use DRM.

About This Document

Data Replication Manager Performance Estimation

These application notes provide a methodology and sample results for estimating the effects of distance on application performance when using the HP StorageWorks Data Replication Manager.

A Microsoft Excel tool has been designed by HP to calculate DRM performance based upon cable distances and packet sizes. To interpret and apply the results of the HP StorageWorks Data Replication Manager Intersite Link Performance Analyzer most effectively, you must understand basic DRM I/O. Then you can show the performance impact on the link distance and speed.

DRM Link Variables

For each intersite link, there are two variables that are chosen during the design process:

■ The distance between the sites

■ The bandwidth of the link

Factors that impact this design are:

■ Latency due to the distance between the sites

■ I/O write rate (number of writes per second)

■ I/O write size (average size in bytes per write)

The performance analyzer tool uses the intersite distance and size of the writes to help in the design of DRM links.

Link Distance

Link Bandwidth

The distance between the sites determines how long it takes for the signal to travel from one site to the other at approximately five microseconds per kilometer per trip. The I/O signal travels the length of the link four times for each I/O transaction. Therefore, the distance will slow down any I/O across the link by adding 20 microseconds per kilometer to the basic zero distance replication.

For long distance DRM, use the driving distance between both sites and multiply that by about 25 to 50 percent. For example, there may be a site where the driving distance is 150 miles and the cable distance is 250 miles. It is the cable distance that needs to be considered and not the driving distance.

The bandwidth determines how long it takes to load the data onto the link. The sum of the start time and the load time equals the time to complete the I/O. The time it takes to load the data onto the link varies depending on the bandwidth of the link and not the length of the link.

Consider how long it takes water to go through a garden hose compared to a fire hose. If each hose is the same length, it will take the same amount of time for the water to come out the other end. Provided each hose can be kept full, the fire hose will transport more gallons per second than the garden hose.

The same physics of distance and pipe size apply to DRM. The time to complete a particular I/O is very dependent on the distance, but is less dependent on the bandwidth. This analogy does not apply in cases of very large I/O and small pipes.

4 Data Replication Manager Intersite Link Performance Analyzer Application Notes

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Hp StorageWorks Data Replication Manager Intersite Link Performance Analyzer

About This Document

Intended Audience

Other Data Replication Manager Documentation

Data Replication Manager Performance Estimation

DRM Link Variables

Link Distance

Link Bandwidth