Sizing Guide Exchange Server 2003 - Fujitsu

White Paper Sizing Guide Exchange Server 2003 Version: 4.2, July 2006
Exchange measurement methodology
The following question is one that is repeatedly asked concerning the sizing of a server: »Which PRIMERGY
do I require for N Exchange users?« or »How many Exchange users can a specific PRIMERGY model
serve?«
This question is particularly asked by customers and sales staff who are of course looking for the best
possible system. Not under-sized so that the performance is right, but also not over-sized so that the price is
right.
In addition, service engineers also ask: »How can I configure the system to enable the best possible
performance to be achieved from existing hardware?« Because, for example, it is decisive just how the hard
disks are organized in RAID arrays.
Unfortunately, the answers cannot be listed in a concise table with the number of users in the one column
and the ideal PRIMERGY system or its configuration in the other column, even if many would like to see this
and several competitors even suggest this. Why the answers to this, what might appear, simple question are
not so trivial and how a suitable PRIMERGY system can still be chosen on the basis of the number of users
is indicated below.
User definition
The most difficult point in the apparently simple question »Which PRIMERGY do I require for N users?«, is
the user himself. One possible answer to the question »What is a user?« could be: a person who uses
Exchange, i.e. who sends e-mails. Is that all? No! He of course also reads e-mails... and the filing option
provided by Exchange is also used ... and addresses are managed… and the calendar is used. And just how
intensively does the user perform this type of task? In relation to the daily requirements …
In addition to the question, what is user behavior like with regard to the number and size of the mail, the
question which is increasingly being asked now concerns the method of access: »How does the user gain
access to the mail system?« A few years ago it would have been normal for really homogeneous
infrastructures to at least be found within an organization unit, and practically all employees would have
uniformly worked with Outlook. Due to the increasing mobility of the end user and the growing diversity of
mail-compatible systems, the multitude of protocols and access mechanisms is on the increase, e.g. Outlook
(MAPI), Internet protocols (POP3, IMAP4, LDAP), Web-based (HTTP) or mobile devices (WAP), just to list
the most important ones.
One could now assume that this would not have a direct influence on the number of users operating an
Exchange server because a user uses only the one protocol or the other one at any given time, and in the
end is only one user. This is however not the case because the mail protocols differ in the method of
communication used. For example, the one type processes mails as a whole and the other type on an
object-orientated basis (sender, recipient, subject, ...).
This different type of access pattern leads to the mail from the Exchange server having to be converted into
the format required. As the information is only stored in one format in the information store of the Exchange
server. The service load caused by the conversion is in part not insignificant. With Exchange 2000 Server
and Exchange Server 2003 and in contrast to Exchange 5.5, Microsoft has already taken several measures
to reduce the load through the conversion of mail formats and protocols. For example, a special streaming
cache is set up for Internet-based access, which relieves the load on the database optimized for MAPI-based
accesses.
We see our greatest problem in the question: How do we integrate the human factor? There isn‟t just a user.
Just as there are small, big, short and thin people, there are users who use the medium electronic mail more
or less intensively. This depends not least on the respective task of the user. Whereas the one user may only
send very few short text mails per day, another user may send mails with larger attachments of several MB.
One user may read a mail and delete it straight away, whereas another will collect his mails in archives,
which naturally results in a completely different load being placed on the Exchange server.
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