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ESE Page Zeroing Enhances Exchange Security

This week I'm on the road at Microsoft Exchange Conference Singapore (MEC Singapore) and MEC Tokyo. This is my first time to visit these locations and a great opportunity to interact with organizations deploying Exchange Server here.

I want to discuss a subject that, up until a few weeks ago, I knew very little about—Extensible Storage Engine (ESE) Page Zeroing. I did some research on this subject to assist with a customer request, and I thought you might like to hear about this database security feature in Exchange Server 5.5. ESE Page Zeroing, also called scrubbing, is a feature that Microsoft first made available in Exchange Server 5.5 Service Pack 2 (SP2). Scrubbing overwrites unused pages in Exchange Server databases with a byte pattern so that a user can't recover data within these unused pages using conventional means. When users delete an item from the Exchange server, such as when they delete a message from their mailbox, Exchange removes references to the item and marks as unused the pages the item was occupying (assuming you've disabled Deleted Item Retention). Without scrubbing, someone can retrieve the deleted data using conventional retrieval methods.

When you enable ESE Page Zeroing, Exchange overwrites the data contained within unused pages with a specific byte pattern during an online backup. After the backup completes, the deleted data is on the tape but no longer in the database, and users can't recover the data using conventional means.

ESE Page Zeroing or scrubbing will usually affect performance when you perform the first backup after enabling the feature. On the initial run, Exchange scrubs every database page, and performance will suffer (backup takes longer and system overhead is greater). However, after the first scrub, the performance effects should be minimal. ESE Page Scrubbing simply checks the timestamp on each page to determine whether Exchange has scrubbed the page and then scrubs the pages that don't have a current scrubbing. Exchange ignores pages that have been recently scrubbed (or if the page has not changed since the last scrub). If you're concerned about the performance effects of scrubbing on the first run, try scrubbing offline (using ESEUTIL /Z) or perform an initial backup to a null device (using backrest.exe from the Exchange Server Software Development Kit—SDK). You can also scrub as a periodic operation every 6 months or so to minimize the effects of scrubbing on performance.

The ESE Page Zeroing feature in SP2 gives us another tool for ensuring that deleted data on our Exchange servers is no longer available and adds a high degree of security for organizations that require it. If you'd like more information on how to use this feature, take a look at Microsoft Support Online articles Q196169 and Q223161.

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