LIS 525 - Estimating Server Needs
To set up a server to work effectively,
you need to know how many requests
it will need to handle at once
(say within 7 seconds)
and how many bytes it will have to deliver per second
at peak times.
How much variation there will be in demand from one time to
will differ depending on the type of site.
For a relatively smooth demand curve,
estimating peak demand at about twice the average
might be relatively safe;
but a site with time-sensitive information
might have much higher peaks.
Once you have an estimate of the peak rate of requests,
you can estimate the peak rate of delivery required
by multiplying the rate of requests by the average file size.
To determine the speed of network connection required in bits per second,
multiply the peak bytes to be delivered per second
by about 11.
if the average file size is 10 Kbytes
and the peak request rate is 0.5 per second (30 per minute),
you need to be able to deliver 5 Kbytes per second
and so require a network connection of about 56 Kbps.
If you are sharing a server
with other information providers,
you still need to be able to estimate total bandwidth usage
over longer periods of time
and you may need to know how many concurrent requests
you want to be able to accommodate.
Many Web hosting plans
specify a maximum amount of data transfer per day or per month
(e.g., 193 MBytes per day or 6 MBytes per month),
after which additional charges apply
(e.g. $0.05 per KByte).
Others may make a general provision
that your traffic should not compromise site performance,
or they may restrict the kinds of files
that you can mount (e.g., no MP3, no software).
Some plans may set a maximum number of requests
(e.g., 10,000 per month),
after which there are additional charges
(e.g., $5 per 10,000).
To determine an acceptable daily traffic limit,
first estimate the peak rate of requests per day
and then multiply that by the average file size.
Add another 10% or more to the byte count
to allow for requests and upload traffic.
Points to Note
Remember that a request for a single Web page
may actually involve many requests for inline graphics files.
On the other hand,
if pages are revisited
or the same graphics are used in multiple pages,
caching at the client side
may reduce the number of bytes
that actually have to be transmitted.
Byte counts may also be reduced somewhat
if HTTP compression is enabled.
Many requests will not be from your intended users.
Quite apart from denial of service (DoS) attacks,
there may be a substantial portion of hits on your site
that do not involve actual use of your information services.
a study by Cooper of about 2½ million sessions
with a Web-based library catalog
found about 27% involving less than 10 seconds of connection
(all these visits were presumed to be from "spiders").
About another 11% of visits
took longer than 10 seconds
but involved no searching.
To estimate storage needs,
one could just add up expected file lengths.
this approach will actually provide an underestimate,
especially when files are small,
because disk space is assigned to files in clusters
(the smallest units
that the operating system allows to be assigned to files).
the smallest file on this course's Web site,
though only 45 bytes long,
still takes up 4096 bytes on a Windows XP hard drive,
because that is the cluster size.
For More Information
- AllAboutYourOwnWebsite.com. 2007.
Bandwidth & Web Space Requirements Analysis -
ALL ABOUT YOUR OWN WEBSITE : Your Guide to Creating and Managing websites.
The definitive how-to,
helping you to design and maintain your own web page.
(Includes calculators for web space and traffic.)
- Cooper, M.D. 2001.
"Usage patterns of a Web-based library catalog".
Journal of the American Society for Information Science
& Technology. 52 (2): 137-148.
- Gromco. 2006.
Web Hosting Menu :
Estimating Bandwidth (Traffic Consumption Calculator).
- K-20 Operations Cooperative. 2007.
K-20 Connected Institutions.
(Links to graphs of usage on school board sites in Washington State.)
Last updated October 17, 2007.
This page maintained by
Prof. Tim Craven
E-mail (text/plain only): email@example.com
Faculty of Information and
University of Western
Canada, N6A 5B7