Guidelines for Sever dimensioning

[Brad Dameron]

We are a large ISP and have several hardware configurations. I can tell you the following configuration and what it is doing in production right now.
 
Pentium 4 3Ghz, 1 GB RAM, 80Gb SATA-I hard drive.
 
It is currently handling a little over 25,000 clients with a 24 hour lease time. This is a mixed OS type of client.
 
In our lab we did many tests and with a AMD X2 6000+ with 4GB of DDR2 800 and a Gigabyte i-RAM ramdisk with 4GB on it we were able to handle upwards of 350k clients. This was using Nominum's dhcperf test too with a 24 hour lease time. 200k customers was achievable with a 250GB SATA-II Seagate enterprise drive.
 
We also had modified the source code slightly to adjust a hash setting. You can find that in the list email. Just search for my name.
 
The AMD processor was ultimately the best for handling DHCP. This is due to how it handles memory. 
 
Also one huge performance enhancement on our linux servers was due to the dhcp logging itself. If you use syslogd you need to look at putting a hypen in front of the path/filename like:
 
# DHCP message into seperate file
local6.*                                                -/var/log/dhcpd.log
 
Or if you don't log to a specific file and log to messages:
 
*.info;mail.none;news.none;authpriv.none;cron.none;         -/var/log/messages
 
If you use syslog-ng then in the conf change:
 
options {
    sync (0);
    
TO:
 
options {
    sync (20);
 
What this does is to only write 20 lines to the log at a time. Instead of writing every line individually. This saves on a lot of disk activity and heavily increases DHCP performance.

 
Brad Dameron
Clearw're
Senior Systems Engineer
 

________________________________

From: dhcp-users-bounce at isc.org on behalf of T Manikandan-Q3926C
Sent: Thu 10/16/2008 11:24 PM
To: dhcp-users at isc.org
Subject: Guidelines for Sever dimensioning



Hi,

 

Can anybody help me in dimensioning the DHCP server?

 

I Have X number of clients to be supported by the server. How will I obtain the CPU, RAM and Hard disk calculations?

 

Say for X number of clients each client takes 4 transactions to get the IP from the DHCP server, considering each packet of size 576 octects, takes 576*4= 2304 octects

For X clients considering 100% client attached during busy hour it will be ( 2304 * X ) octects, or (2304 * X *8/3600) bytes per second, which is the bandwidth but, 

How should the dimension be for the CPU, RAM and Harddisk. ( Taking account for OS , especially for RHEL),

 

Regards

Mani

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