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Windows XP has a problem writing to Windows 2000 and NT servers under certain conditions, according to two developers of mission-critical applications. The problem has led to maddening errors, and these companies are challenging Microsoft to solve it.
The clash is a bit like two ants taking on an elephant. However, the ants in this case have the weight of evidence on their side. The company that has taken the lead in this dispute is Tangent Systems. Tangent produces DocuTran II, an imaging and data capture application used mainly by financial institutions for check processing, payment handling and other tasks where accurate scanning is an absolute requirement. A large Tangent customer typically has hundreds of employees using PCs to write document images to fixed-disk storage on several servers.
The back end can be Windows 2000 Server, Windows NT Server or NetWare.
A few months ago, some DocuTran users began complaining that their workstations were showing error messages and their servers were losing data. To make a long story short, Tangents software development manager, Dave Berkowitz, found after extensive testing that delayed writes from Windows XP clients to the server disks were intermittently causing data loss.
The data loss was observed only when Windows XP clients were writing to Windows 2000 or NT servers using SMB signing. (Server Message Block signing digitally signs data packets on a network.) The problem never occurred when the server was NetWare, whatever the client, or when the client was Windows 2000 Professional, whatever the server.
Tangent decided to go public with its findings after what it believed was a lack of responsiveness from Microsoft. The Tangent developers who conducted the testing posted a report and a free utility, Dlaytest.exe, so that any enterprise can test its own hardware and software configuration for the problem. (To download the utility, go to www.bri.li/3501).
Microsoft responds
According to article 321733 in Microsofts online Knowledge Base, writing a file to a server across a network can generate this error message: “Windows was unable to save all the data for the file x. The data has been lost.” The article says this has been confirmed as a problem with Windows 2000 Server and Windows XP Pro and Home clients.
Another Knowledge Base article, 293842, says that data loss can occur “under extreme file system stress” but that this was corrected in Windows 2000 Service Pack 3 (released Aug. 1, 2002).
A Microsoft spokeswoman had this to say: “We did work to resolve the issue fully with Service Pack 4 for Windows 2000 on the server and Service Pack 1 and the available hot fix identified in KB 321733 applied to Windows XP. Microsofts testing shows that when the SP1 and hot fix are applied to these [XP] machines, that the issue is resolved. Again, we will be working with this customer directly to help resolve their specific issue.”
Tangent product specialist Dan Michalski, who conducted much of his companys original testing, disputes the idea that SP3 or SP4 for Windows 2000 eliminates the data loss. Michalski said hes seen the error on SP4 simply by writing data files from XP with Dlaytest.exe while refreshing a view of the files in Windows Explorer every few seconds. “Were talking about a single server thats completely dedicated to this test and one workstation,” he said. “I wouldnt call that extreme stress.” This finding is supported by a similar report from insurance software company Applied Systems.
Tangent and Applied Systems indicate in their reports that disabling SMB signing ends the data errors. If your files are still experiencing data loss after applying the service packs and hot fixes mentioned earlier, you can turn off signing using Group Policy and a setting described in article 321733.
The big question for Microsoft is why it imposes delayed writes on server disks at all. An enterprises priority is to get transactional data committed—without fail. Delayed writes, an old disk-cache trick, are a luxury that should be trumped by reliability. Any transient gain isnt worth your pain.
Brian Livingston is editor of BriansBuzz. com. His column appears every other week in eWEEK. To send tips, visit www. briansbuzz.com/contact. Send your comments to [email protected].