In some cases, Windows Server 2003 might not be able to perform backup to a tape device over a SAN because of a
conflict with one of the features in Plug and Play. This is a subset of a problem with Remote Storage Manager (RSM) that can interfere with -- or even block completely -- the flow of data to a tape backup unit over a storage area network (SAN).
The problem is that Windows Server 2003's RSM sends a SCSI signal called Test Unit Ready (TUR) to a "removable" backup device (which it thinks the tape library is) every second to check the status of the device. Unfortunately, this process doesn't work well over a SAN and can even interfere with the backup operation.
Microsoft has three workarounds for this problem, two of which require modifying the Registry. The first is to disable all TUR requests for a tape service; the second is to disable the TUR requests for specific devices in a tape service.
The third workaround is to programmatically disable TUR requests for specific devices. This is done by calling DeviceIoControl with the IOCTR_STORAGE_MCN_CONTROL I/O control code. This method is more complex, but offers the possibility of better control. Microsoft provides specific information on how to do this in its online library.
Hewlett-Packard Co. also has a workaround that involves starting and then stopping the Removable Storage service every time the server is restarted. According to Microsoft, this remedy works because the service makes the DeviceIoControl call to all tape devices when the service is stopped. Hewlett Packard describes this workaround in a tech support document that includes further information on the problem.
Microsoft's description of the problem and the workarounds can be found here.
Rick Cook has been writing about mass storage since the days when the term meant an 80 K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last 20 years he has been a freelance writer specializing in issues related to storage and storage management.
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