How Did ISA 2004 SP2 Eat Up 400MB of Disk Space?

If you’re running low on disk space, you might want to know that ISA 2004 SP2 just might push that disk over the edge. It might not seem obvious that the ISA 2004 SP2 file, which is only about 12 MB in size could eat up 400+ MBs of disk space. Its not the update itself that takes up the space, its the new ISA error-level tracing feature. The tracing mechanism runs continually in the background and Microsoft PSS can use this information to troubleshoot your ISA firewall installation.

Don’t worry, there is no personally identifiable information contained in the file.

Tracing takes place in the background, and has a nominal effect on ISA firewall performance. A 400 MB file is placed in the %windir%\debug\isalog.bin is created by Service Pack 2 and this file contains the tracing information.


Microsoft recommends that you use the default settings for this feature. However, if you want to modify the tracing feature, you can do so using the registry key HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ISATrace. To change the size of the file used by tracing, change the value of CircularlLogSizeMB. To disable tracing, change the BootTracing value to 0. This does not delete the file, which has to be deleted manually. After registry changes, restart the computer so that the changes take effect. If you create the registry key before installing Service Pack 2, and set the BootTracing value to 0, the tracing file will not be added during the installation, and tracing will not be enabled.

For more information on Service Pack 2 improvements for the ISA firewall, check out the ISA 2004 White Paper over at



Thomas W Shinder, M.D.




MVP — ISA Firewalls

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