Tech Line
RoboCopy Reassurance
How RoboCopy decides what to replicate.
Chris: Thanks for passing the info on robocopy.exe during
the TechMentor conferences. The content mentioned in the robocopy.doc
file doesn't tell me what I'm looking for. I'm trying to find out whether
robocopy compares the "create date/time," "modified date/time,"
or "accessed date/time."
Please let me know how to resolve this issue. Thanks!
— John
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John, I completely understand your confusion. RoboCopy.exe
is a Windows Resource Kit Tool that can copy folders, folder trees, and
files from a source to a local or remote destination. Many organizations
use this feature as a quick and dirty way to replicate select file server
content to another box. For those of you not familiar with RoboCopy, you
can download this tool along with the other Windows Server 2003 Resource
Kit Tools at the Windows
Server 2003 Resource Kit Tools page. Once downloaded and installed,
you will find the 35-page RoboCopy.doc file in the Resource Kit installation
folder. By default, this file can be found in "C:\Program Files\Windows
Resource Kits\Tools" folder. This file documents the vast array of
options available for this tool, as well as many gotchas.
If you're wondering why I'm in agreement with John in his confusion,
take a look at the RoboCopy.doc file. While it's a very thorough reference
with plenty of excellent examples, it also contains some of the phrases
that make network administrators cringe. Here are a couple of my favorites:
- "In most situations, Robocopy includes these files by default"
(page 16)
- "…some files and directories (such as skipped Same files)
might remain in the source tree even when /MOVE is specified" (page
22)
When I hear "In most situations," my first instinct is to wonder
about the non-most situations. So the bottom line with RoboCopy is that
it may not be a perfect replication tool, but it is free. With proper
testing and tweaking, you can arrive at a reliable replication tool for
select folders on file servers.
Now to answer your question, when RoboCopy replicates files from a target
to a destination, its primary replication criteria is Modified Time. If
the file on the source is newer than the file on the target, the source
file will be replicated. While the Modified Time attribute is usually
sufficient to make a "replicate" or "do not replicate decision,"
if both files have the same modification time and the source file is larger
than the target file, the source will overwrite the target. Any newly
created files in the folder being copied via RoboCopy would also be copied.
If you're looking to constantly monitor a folder and replicate files
as soon as they are modified, you can use the /MON:n switch. With this
switch, RoboCopy will run in the background and after the number of changes
specified by the n variable occur, RoboCopy will copy the source files
to the target. For example, when executed with /MON:5, after 5 files in
the directory tree are modified, those five files would be replicated.
This allows you to control replication so that it occurs in bursts. If
you are replicating over a WAN and want to limit the times that RoboCopy
runs, you can do this by running the command with the /RH:hhmm-hhmm switch.
This allows you to setup a time window in which RoboCopy will replicate
files. For times outside the window specified by the /RH switch, RoboCopy
will sleep.
For more information on RoboCopy, the RoboCopy.doc file mentioned earlier
is a good start. Also, if you're looking for a tool that can help you
create RoboCopy replication scripts, take a look at RoboCopy
GUI 3.0.1. This GUI tool can be used to create a RoboCopy command
and save it as a batch script. The GUI tool is not the most intuitive,
with each switch just listed as a checkbox in the RoboCopy GUI window,
but with a copy of the RoboCopy.doc file handy, you can easily look them
up.
Happy RoboCopying!