ACAD (Any) : Problems with Saving = Network Timing Issues

Originally Posted by Hendie

Have you had drawings you were working on change to “Read Only” for no apparent reason ?
AutoCAD goes and tells you that the file is being accessed by another session when you know for a fact that you are the only person working on that particular drawing.
The only way out is to do a “Save As”, exit, delete the original, rename the copy and start up again.

Originally Posted by Jason Martin
(Thanks should go to JM for the great explanation)
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The problem might be a "NETWORK TIMING ISSUE". The fix for this problem is illusive and sometimes expensive (new servers, additional servers, faster networks, more isolated (switched) networks, etc). Some Autodesk people have indicated that every time that they've seen this (actually seen it, at a customer site) the solution was to increase client to server throughput. Without fail, that's been the solution. The problem is more evident with AutoCAD, because of the complicated write procedures. There are more chances for things to fail with so many file locks, un-locks, and renames. Autodesk's file write method is completely compliant with Microsoft's API requirements, but when the server doesn't respond within the designated period, the write fails (actually the rename fails) and the user is left with a temp file.
The basics of the AutoCAD save procedure is:
1.
AutoCAD verifies the file lock that it created previously (either at file open or on last save)
2.
AutoCAD creates a new temporary file, and locks it. The current drawing information is written to the temporary drawing.
3.
AutoCAD deletes the .bak file.
4.
AutoCAD sends a remove lock request for the original .dwg.
5.
AutoCAD tries to rename the .dwg to a .bak. General problem location: Usually when a read only occurs the server has not completed the remove lock request. The rename is then treated as a sharing violation and the rename request is denied by the server.
6.
AutoCAD unlocks the temporary drawing.
7.
AutoCAD renames the temporary drawing to the original drawing name. The read only problem can occur here as well, as if the file lock is not removed before the rename request is made, there is a sharing violation and the rename request is denied.
8.
AutoCAD then re-locks the original drawing name.

Things that can cause these problems are as follows:
Very fast workstations and a "slow" server.
Network saturation
Excess server workload
Virus protection on the client
Virus protection on the server
"Misbehaving" network drivers on the client or on the server.