Chapter 9 from the book of Humphrey Sheil suggests to put in deployment diagram chapter, in a
vendor / machine agnostic way, the resources expected to be deployed in order to support the
architecture and then to provide concrete examples of a specific vendor / machine combination.
How can I guestimate resources based on concurrent user number and performance requirement?
Chapter 9 say also: "we expect the combined web / application servers to require different system resources to the database tier"
It is reasonable but I have some ideas about web and app resources but I do not know how to estimate resources for database machines?
CPU, RAM and network speed of database server have to be less or more than web and app server?
You can start by looking @ hardware requirements of standard database servers .These are typically present on product sales sites.
For example, you can look at the database recommendations of Oracle RAC and then interpolate from there..
Personally, even in real life, i have found it difficult to recommend a particular server brand (due to lack of knowledge)..but its easier to recommend RAM,CPU Clock Speed,etc.Note that you have an option to go for a higher hardware..(standard old style database servers) or lower configuration homogeneous database servers..(again Oracle RAC)
Of course you will have to read a bit..the final recommendations would depend on your choice of database implementation....
...database servers would definitely have more juice than web servers...on all fronts(CPU,RAM,HDD)..
Compared to App Servers..it depends on a host of factors..such as type of database configuration, if you intend to share resources on App/DB level,etc...there is no right/wrong answer in my opinion...a politically correct answer would be to say..database config might be slightly higher than the app config..
OCMJEA/SCEA, SCDJWS, SCBCD 1.3, SCJP 1.4
My SCEA experience:http://javalogue.blogspot.com/