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XADM: Storage Capacity Limits of Microsoft Exchange Server

This article was previously published under Q143376
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The capacity limit for a Microsoft Exchange Server server-based InformationStore is 16GB. This could be all in one folder, or split up among manyfolders. A Microsoft Exchange Server generally hosts one PrivateInformation Store (16GB for all Mailboxes), and one Public InformationStore (16GB for all public folders).

Personal Folder stores have a theoretical maximum of 2GB total storage.This could be all in one folder or split among many folders. The limit tothe number of messages (objects: messages, folders, files, etc.) in aPersonal Store is 16K.
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A Microsoft Exchange Server can be configured as a private only, publiconly, or public/private Server. There is a limit of 16GB on any MicrosoftExchange Server for the private database (DB) and a different 16GB limitfor the public DB. Therefore, a public/private Microsoft Exchange Servercan house 32GB of storage, 16GB of which is for the private DB and theother 16GB for the public DB.

If you have a large Public Folder, you can dedicate a single MicrosoftExchange Public Folder Server to house the data for that one Public Folder,so the limit for the size of a single Public Folder is 16GB.

Microsoft Exchange performs single instance storage in the database on aMicrosoft Exchange Server, so the 16GB limit on the private database isreally a much larger logical storage. Single instance storage means that if1000 users on a Microsoft Exchange Server get the same message, the messageis only stored once in the database and each of the users gets a pointer tothe message. The same single instance storage also holds for attachments.If a user opens their copy of a message and modifies it but they don'tmodify the attachment, Microsoft Exchange doesn't resave the attachments,just the new message body.

The Microsoft Exchange beta sites saw at least 3:1, and sometimes upwardsof 6:1, single instance storage rates because most messages have an averageof between 3 and 6 recipients. To extend this, the logical storage limitfor users on a single Microsoft Exchange Server is at probably least 16GB*3and possibly upwards of 16GB*6.

Another factor to consider is how many people use Personal Folders (.PSTfiles) as their delivery store. If users are using Personal Folders, theMicrosoft Exchange Server can handle more users. The time at which thelimit is reached for storage in the private DB on a specific MicrosoftExchange Server will depend on the pattern of usage by the users.

By default Microsoft Exchange sets up circular logging on the Directoryservice and the private and public DB's. What this means is that as thetransaction log files get flushed to the databases, they are deleted. Thebeta sites saw, on average, no more than 4 logs files, each of which wasMB. So in the default install configuration, log file growth will not be afactor. If an administrator configures their Microsoft Exchange Server notto use circular logging, the log file growth will be based on the number oftransactions that are occurring on the Microsoft Exchange Server. This isbased purely on activity.

Article ID: 143376 - Last Review: 10/26/2013 01:20:00 - Revision: 4.0

Microsoft Exchange Server 4.0 Standard Edition

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