Watch out for negative side effects of the /3GB boot.ini switch

Just because something has been working without any glitches for a long time, don't assume that it won’t create a problem.

Most Exchange administrators are familiar with the /3GB boot.ini switch that increases the amount of user-mode process space from the standard 2GB to 3GB. The use of this switch leaves 1GB of virtual address space available to the operating system. The /3GB switch reduces the amount of memory fragmentation in Exchange's store.exe process. While the use of the switch is often necessary for maximum performance of your Exchange server, it can have a troublesome side effect, particularly as you attempt to recover from a database problem in one of your storage groups. In fact, my IT group encountered one such problem just recently.

After a communication glitch with a SAN resulted in the corruption of one of our three storage groups, my team worked all day with eseutil and other utilities to attempt to repair the storage group’s database. While the process was ultimately successful, the repaired database was written to a local disk and not to the SAN. During the attempt to move the .edb and .stm files to the SAN, we encountered the error "Insufficient system resources exist to complete the requested service." Puzzled, we tried a variety of methods to move the data to its final location.

Ultimately, we stumbled across a solution: We removed the /3GB switch from the boot.ini file, rebooted the Exchange server and tried the file copy process again. This time, we were successful and the Exchange server was placed back into production.

The lesson: Everything is a possible culprit! Just because something has been working without any glitches for a long time, don’t assume that it won’t create a problem.


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