Last week, I started a discussion about Exchange Server database maintenance and the tools we have available to detect and recover from physical corruption. This week, let’s turn our focus to logical corruption and the ISINTEG utility.

Logical corruption of your Exchange Server databases is problematic and much more difficult to diagnose and repair than physical corruption. The user and administrator are typically unaware of a logical corruption occurrence. To make matters worse, Exchange Server contains no built-in checking (like that available for physical corruption) to diagnose and alert you about logical database corruption. No specific symptoms identify logical corruption. Often, when an administrator discovers the logical corruption, it's too late for repair.

A bright spot is the existence of tools that can repair logical corruption of Exchange Server databases. Logical corruption occurs at either the Information Store (IS) level (tables, indexes, keys, links) or at the database level (B-Tree structures), so we must have tools that address each of these levels. The ISINTEG utility finds and eliminates logical corruption at the IS level; ESEUTIL checks, diagnoses, and repairs problems at the database level.

ISINTEG repairs errors in Exchange Server ISs that might prevent the database from starting or mounting or prevent users from accessing their data. ISINTEG is useful for restoring Exchange Server databases to normal operation but you shouldn't consider it an IS maintenance tool. You can use ISINTEG only when a database has been damaged and only with the help of Microsoft Product Support Services (PSS). Because ISINTEG focuses on the logical level rather than physical database structure, it can repair and recover data that tools such as ESEUTIL can't. When looking at the physical database level, ESEUTIL might find the data to be valid because it looks for things such as page integrity and B-Tree structure. Data that appears valid to ESEUTIL from a physical view of the database might not be valid from a logical view. For example, data for various IS tables, such as the message, folder, or attachments table, may be intact, but the relationships among tables or records within tables might be broken or incorrect because of corruption in the logical structure. This corruption can render the database unusable. ISINTEG can often repair this logical schema corruption when other utilities might not even be aware of the problem.

Database corruption in Exchange Server is relatively rare—especially if you have solid hardware and practice good configuration management. However, if and when these problems do occur, you need to be armed to respond. Take time to learn the tools and to practice recovery and repair. As always, use these utilities with caution and under the advice of Microsoft PSS.