What size server do I need?

Course Data

When an exercise, lesson, test or survey is saved ready for upload to NetSeries it is created as a single file. You can right-click on this file and select Properties to see its size — this is the size of the lesson, test, exercise or survey, and this is how much data will be transferred each time a student / trainee uses the material. It is also the amount of space that will be taken up on the hard disk.

Lessons, tests and thelike can vary greatly in size. Key determinants of size are whether sound and/or video has been included. The use of many large graphic images will also affect the size of the file. However, well-constructed materials are often between 200Kb and 500Kb in size. For the sake of simple calculations we will assume that all materials are 350Kb in size.

If we assume there are two courses, and each course has 20 modules (20 lessons, exercises, tests and surveys) then the total amount of space needed for the course materials is:

350Kb × 20 modules × 2 courses = 14Mb

With hard disk capacities for even desktop computers in the hundreds of gigabytes it is apparent that there is no need to worry about the space required on the hard disk for the course materials.

Results Data

As a rough guide, each individual's data takes up about 1Kb of disk space, plus 2 Kb for each result. This 2Kb is a very general estimate, because Question Tools stores every answer every user ever makes, and so many long text answers can lead to much larger space requirements. However, if we continue to assume 2Kb of data per result, then if the student / trainee takes 40 modules (40 lessons, tests, exercises and surveys) this individual's data will take up about 80Kb of disk space. If there are 2,000 trainees / students then their data will require:

80Kb × 2000 = 160Mb

Again, with hard disk sizes increasing every month this is a relatively small figure — it would occupy just 0.1 percent of an 80Gb hard disk.

Data Transfer

Moving data across a network is a much more pressing issue. If we have 2,000 trainees / students each viewing 14Mb of data then in total they will transfer 28Gb of data across a network while completing their two courses. This may sound large, but the average modem works at 44 Kbs (thousand bits per second - about 5.4 Kb of data per second), and if left running can transfer 13Gb in a month.

The Key Issue: peak Data Transfer Rates

The real issue is the network, and how many users will try to access the materials at the same time. If 2,000 trainees attempt to access the materials at the same time we know from tests that NetSeries will cope, but the network connection almost certainly will not. If 100 trainees / students take a test at the same time over a 20 minute period they will transfer 35Mb of data — just under 2Mb per minute.

Which Server?

NetSeries is multithreaded and so can take advantage of computers with more than one processor. However, NetSeries has been created using C++ and is very fast — handling most requests for complex, custom-generated pages in under 0.001 seconds on a single-processor desktop machine. The power of the server is unlikely to be a bottleneck. In most cases a single-processor machine, with just one processor, a copy of Windows XP, and a couple of reasonable hard disks will be perfectly adequate.

Summary

The key issue is not whether NetSeries can cope, nor the power of the server, but whether your network can transfer the data. To answer this question you need to know how many trainees / students will be logged on at peak times, and how much data your network can reasonably transfer per minute.

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