Redirector Uses Core Mode on Large File Transfers (119870)
The information in this article applies to:
- Microsoft Windows NT Workstation 3.5
- Microsoft Windows NT Server 3.5
This article was previously published under Q119870 SYMPTOMS
When you copy a large file to or from a Windows NT Workstation and Windows
NT Server version 3.5 computer, the redirector may switch to core mode
during the transfer. The use of core mode increases the time required to
transfer the file. The switch to core mode occurs after approximately 20
megabytes (MB) have been transferred and is more likely to occur when
transferring a file to a Windows NT server, but it can occur in either
direction. Core mode over FDDI requires more bandwidth than over Ethernet
or token ring, so the symptoms are more pronounced on fiber. Smaller files
transfer in raw mode.
CAUSE
Raw I/O requires exclusive access to the virtual circuit, meaning the
virtual circuit must be effectively "locked" for the duration of the raw
I/O. If other activity is occurring on the circuit at the time the
redirector tries to do raw I/O, the circuit cannot be "locked" so the
redirector uses core I/O instead.
One reason the virtual circuit cannot be "locked" is that as the file data
is being written, the file also needs to be extended which also requires
network activity.
The reason the problem surfaces at a large offset into the file has to do
with when the lazy writer and modified page writer start their work. When
the system starts running short of free pages, the modified page writer
wakes up. Unfortunately, the modified page writer likes to write one page
at a time. The redirector cannot turn a 4K write into a raw I/O.
The correction to the problem will require changes to both the
redirector and the memory manager.
RESOLUTION
A new redirector is in the works, but will not be ready for
at least a year. It will not be corrected in the final release
of Windows NT 3.5.
STATUS
Microsoft has confirmed this to be a problem in Windows NT version 3.5. We
are researching this problem and will post new information here in the
Microsoft Knowledge Base as it becomes available.
| Modification Type: | Major | Last Reviewed: | 10/23/2003 |
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| Keywords: | KB119870 |
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