Exchange Server Database Errors: Patch That Page!
23.05.12
Is so pervasive in the Exchange world; it's part of the documentation and online help for Eseutil and
Isinteg (remember those?), to cite just a couple of instances. However, it's a little misleading to think of an .edb file as nothing more than a
collection of pages because the information on those pages is interlinked. Losing a single page can have effects ranging from minimal to
catastrophic-it all depends on which page you lose.
ESE uses a number of mechanisms to protect against page-level corruption. For example, each page contains a checksum that's generated at the time the
page is written. Any time you want to know if a page is valid, you can read the page data, compute a new checksum, and see if the new value matches the
stored checksum. That's exactly what happens during streaming ESE backups in Exchange 2007, Exchange 2003, and Exchange2000.
In Exchange 2010, a background maintenance task scans each page and performs the checksum check; the process is scheduled such that every page of every
database, on both active and passive copies, should be scanned at least once every seven days. The checksum operation is throttled so that it doesn't
read more than about 5MB/second worth of data, so its I/O impact is light. You can change this behavior so that checksum scans take place during the
regular database maintenance window, but Microsoft recommends that you leave the default behavior in place.
Source: Windows IT Pro