This article describes the scalability factors and limitations of Volume Shadow Copy Service (VSS) when used on an Exchange 2003 32-bit operating system (OS) identified by Microsoft , and provides resources and recommendations for resolving them.
Microsoft has identified resource challenges for Exchange 2003 on Windows 32-bit OS when Microsoft Volume Shadow Copy Service (VSS) is creating and/or holding open a volume snapshot. Since Replay uses the VSS technology, when our backup runs, the same constraints exist. The limitation of available paged/non-paged pool memory in a 32-bit system is noted by Microsoft. Microsoft Technet has provided a document titled “Scalability Factors for Shadow Copies” to cover this topic. There are several ways to reduce resource usage, which will be covered in these helpful links and the body of this document.
32-bit Resource Limitation
Search Microsoft Technet for the following article for more information about the constraints in this environment and some possible ways to reduce resource consumption:
“Scalability Factors for Shadow Copies”
Microsoft Support noted some of the symptoms of resource exhaustion in the following article concerning the impact on IIS:
“Users receive a “The page cannot be displayed” error message, and “Connections_refused” entries are logged in the Httperr.log file on a server that is running Windows Server 2003, Exchange 2003, and IIS 6.0”
The above article identifies an error to look for in the IIS Httperr.log file that indicate there are no more possible connections available. There may be multiple occurrences of entries that resemble the following:
If Exchange is refusing connections, this is an indicator that pool memory has been exhausted.
Unfortunately, it is difficult to predict or detect without actually pushing the system into the actual conditions that may cause an outage with Exchange. To determine if there is a scalability issue, perform any of the following procedures.
If you determine that there is a scalability issue, follow the Recommendation provided.
Running vshadow from Microsoft can help determine the load that VSS will generate when a volume shadow copy is created without using Replay. Vshadow is a sample application for developers provided by Micorosoft in their VSS Software Developer’s Kit. Replay installs a copy of this tool which allows the shadow copy it creates to persist (meaning once the volume shadow copy is created, it will remain open for a configurable amount of time).
To run vshadow:
Monitoring Pool Usage
You can monitor pool usage in various ways prior to implementation of a VSS backup strategy.
To monitor pool usage:
The best recommendation is to move to a 64-bit operating system which does not have the aggressive paged/non-paged pool memory limitation which is found in a 32-bit operation system. This may become a good opportunity to provision a new 64-bit Windows 2008/R2 OS and upgrade Exchange to 2007 or 2010. Even migrating the existing Exchange 2003 server to a Windows 2003 64-bit server can resolve the issue. It is also important to note that VSS technology is stated to be the method used for protecting Exchange 2010 by Microsoft. Backing up on a mailbox level is not the method desired for Exchange 2010. Given this direction, it may also be a good point to evaluate upgrading the OS or Exchange version instead of investing in other non-VSS alternatives as a backup solution.
If migrating to a 64-bit operating system is not an option, refer to the following suggested workarounds.
Before you begin, adhere to the following prerequisites:
If Replay is in place, an immediate alleviation to the issue may be found in the configuration changes noted below: