Another network requirement is that your forest's schema master and at least
one Global Catalog (GC) server must be running Windows 2003 SP1; again, the
Standard or Enterprise Editions are both acceptable. One final requirement to
be aware of, particularly if you're adding Exchange 2007 to an existing organization,
is that Exchange 2007 can't exist in the same organization as Exchange Server
5.5.
Calculating Your Memory
Determining the appropriate amount of memory for an Exchange 2007 server takes
a little bit of work. Microsoft provided guidelines for how much memory Exchange
2003 required. Over time, though, it became obvious that the general rule of
thumb for an Exchange 2003 server was to install as much memory as your server
would accommodate. This simply isn't the case with Exchange 2007. Although Microsoft
has issued minimum and recommended memory configurations for each server role,
the company has also stipulated the maximum amount of memory that should be
installed in an Exchange 2007 server. Of course, exceeding the maximum recommended
amounts of memory isn't usually a problem; Microsoft specifies these caps because
you won't see additional benefits to performance by using more than these amounts.
As if setting maximum limits on server RAM weren't unusual enough, the memory
recommendations vary depending on the roles the server is hosting and on the
number of processor cores installed. For example, Microsoft recommends that
you install a minimum of 2GB of memory into an Edge Transport server. However,
if the server contains more than two processor cores, Microsoft recommends adding
1GB of memory for each additional core beyond two. As such, the recommended
amount of memory for an Edge Transport server with four processor cores would
be 4GB. A simpler way of stating this recommendation is 1GB per processor core,
with a 2GB minimum. Table 2 shows Microsoft's
recommended memory configurations for each Exchange 2007 role.
You might notice that Table 2 doesn't
list minimum or recommended memory amounts for Mailbox servers or for servers
hosting multiple roles. Microsoft's recommended memory amounts for these types
of servers are based on how heavily the server will be used. If a server is
hosting multiple roles, and the Mailbox server role isn't among them, you can
safely use 2GB as a minimum amount of memory, and the server should function
reasonably well with 4GB of memory installed. If the server is hosting the Mailbox
server role, though, these recommendations don't apply.
The first thing to consider when installing memory for a Mailbox server role
is the number of storage groups (SGs) that will reside on the server. The required
amount of memory increases as the number of SGs hosted on the server increases.
Table 3 shows Microsoft's minimum recommended
memory for Mailbox servers by the number of SGs hosted on the server. The amount
of memory shown in Table 3 isn't the
total amount of memory you'll need but rather is a base memory amount from which
to begin calculating the actual amount of memory required by the server.
The next thing to consider is the anticipated mailbox-usage pattern of your
users. Microsoft defines a light email user as someone who sends 5 messages
and receives about 20 messages a day. An average email user sends about 10 messages
per day and receives 40 messages. A heavy email user is someone who sends as
many as 20 messages a day and receives as many as 80 messages. Anyone who uses
email more than that would be considered a very heavy user. For light use, Microsoft
recommends adding 2MB of memory per mailbox; for average use, 3.5MB per mailbox;
and for heavy use, 5MB per mailbox. Keep in mind that these values are in addition
to the recommended base memory that Table
3 shows.
To see an example of calculating mailbox memory requirements, suppose your
organization had an Exchange server with one SG that hosted 100 mailboxes. Just
to keep the math easy, let's say that 25 of the users were light users, 25 were
heavy users, and 50 were average users. Table
4 shows how you'd calculate the memory requirement in this scenario. Of
course, you can't install 2,398MB of memory on a server; you'd need to round
the number up to the next viable amount of memory. Depending on the server's
system board, you'd need either 3GB or 4GB.
Finally, you must take one additional factor into account before deciding how
much memory to install on the server: Will the server be performing local continuous
replication (LCR)? LCR consumes both memory and CPU resources. If you're going
to use LCR, Microsoft recommends adding an additional 1GB of memory to the server.
While I'm on the subject, LCR places approximately 20 percent of additional
overhead on the server's CPU because the Microsoft Exchange Replication service
copies and replays in logs to the passive copy of the database. Therefore, you
might want to consider adding an extra core or a faster processor if LCR is
in use.
Using Your Disk Resources
The last thing I'll talk about is disk resources. Table
5 lists the minimum amounts of hard disk space that an Exchange 2007 deployment
will consume. The rules for servers that are hosting the Mailbox server role
are similar to the rules used in Exchange 2003. Basically, databases and transaction
logs should be stored in separate locations for both performance and fault-tolerance
reasons. Also, volumes containing Exchange databases or transaction logs must
be formatted as NTFS; FAT and FAT32 file systems are not supported. You might
also consider storing databases or transaction logs on a RAID array. RAID 10
arrays are usually a good choice because they offer the performance of RAID
0 with the mirroring of RAID 1. If you're using LCR, you'll also want to dedicate
additional volumes to the replicated transaction logs and databases.
Ready for Deployment?
As you can see, Exchange 2007 has some rather stringent hardware requirements.
For a quick reference, take a look at the checklist, "Exchange 2007 Infrastructure
Requirements," page 60. It's important to make sure your proposed hardware is
adequate for running Exchange 2007 and that it allows for a reasonable amount
of future growth. When these basic requirements are met, you should be ready
for your Exchange 2007 deployment.
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