I agree with Roady's opinion. Due to the Exchange database storage
structure, it is not easy to estimate the OST file size preciously.
Generally, the database size will be larger than the actually file size
saved in the mailbox. It is the same for the OST file as it a cache of
Exchange database.
Because of the Single Instance Storage feature, one message can belong to
many mailboxes. For example, if you send a message to several recipients
who reside on the same Exchange Server computer, the message is only stored
once in the information store, and the recipients just receive a pointer to
the message. If one recipient deletes the message from his or her mailbox,
the message is not deleted from the information store, only the pointer to
it. The message itself is not deleted until the last recipient deletes it.
This also means that all messages associated with a user may not be removed
from the Exchange Server computer when you move the user's mailbox to
another Exchange Server computer. The message sent to several recipients
will remain on the Exchange Server computer until all recipients of the
message have been moved to another Exchange Server computer or they all
delete their pointer.
The Exchange database engine uses sector level allocation. Every operation
that requests new memory and requires that a new extent be allocated, is
given a new extent of 16 pages (a page is 4 KB) -- regardless of the actual
number of pages being requested (may be one page). This leads to a
relatively sparse database structure. Therefore, it's generally true that
the size of an Exchange database will always be larger than the amount of
data it contains.
However, we have a workaround to limit the OST file size on local machine.
So that we can ensure it would not be "too large". Please refer to:
832925 How to configure the size limit for both (.pst) and (.ost) files in
http://support.microsoft.com/?id=832925
Hope it helps.
Regards,
Pat Cai
Microsoft Online Partner Support
Get Secure! -
www.microsoft.com/security
=====================================================
When responding to posts, please "Reply to Group" via your newsreader so
that others may learn and benefit from your issue.
=====================================================
This posting is provided "AS IS" with no warranties, and confers no rights.