Guidelines for Sever dimensioning

[T Manikandan-Q3926C]

Hi Simon,

  Considering the fact clients are CPE (customer premise equipments)
somewhat like a Modem with a Linux OS, which is obtaining the IP address
from the DHCP server (for a lease of 10 hours) connected via a L3 switch
(acting as a relay) in case of the Controller of the CPE is down for
some reasons all CPE will reboot and require the IP address (is that
correct?)
  So the server dimensioning has to be on the worst case scenario/ Busy
hour in case of the Busy hour say for example 60% of client is connected
to the system and in case of worst case 100% of clients is connected to
the system, this is our assumption, correct me if I am wrong.
 
Regards
Mani

-----Original Message-----
From: dhcp-users-bounce at isc.org [mailto:dhcp-users-bounce at isc.org] On
Behalf Of Simon Hobson
Sent: Friday, October 17, 2008 12:32 PM
To: dhcp-users at isc.org
Subject: Re: Guidelines for Sever dimensioning

T Manikandan-Q3926C wrote:

>Can anybody help me in dimensioning the DHCP server?

Try the archives - it's been discussed a few times !

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

Sorry, but you can't. There are just too many variables to say X 
clients need Y hardware.

How long are your leases ? Minutes, Hours, Days, Weeks - longer 
leases put less load on DHCP server.

What mix of clients do you have ? Some (Windows) send loads of DHCP 
Informs which add extra load. Some (most printers, Mac OS X) don't 
retain a lease across restarts so NEED the DHCP server to come alive 
when switched on in the morning). Some clients (Windows) will quite 
happily keep their existing lease and start up on the same network 
with the old address if they can't contact the DHCP server.

What pattern of use do your clients have ? A rigid working 
environment where several thousand PCs all get switched on between 
8:20 and 8:30 is very different from one where they get switched on 
at random times as people come and go on flexitime. We once had a 
query from someone considering (IIRC) something like 50,000 clients 
and bothered about a statewide power outage - and all 50,000 clients 
wanting an address at the same time.


 From previous discussions, it would seem that a significant 
constraint is disk performance. You can minimise this by various 
techniques - in extreme putting your lease file on a solid state disk 
(eg battery backed ram disk). Network load is unlikely to be a 
constraint, and normally CPU loading isn't a problem either.