--- title: "Robocopy /MIR: Sync Files with Ease and Confidence" description: "Understand the robocopy /MIR switch and learn how to sync files with numerous examples in this easy-to-follow guide." canonical: "https://adamtheautomator.com/robocopy-mir/" --- # Robocopy /MIR: Sync Files with Ease and Confidence > Understand the robocopy /MIR switch and learn how to sync files with numerous examples in this easy-to-follow guide. Source: https://adamtheautomator.com/robocopy-mir/ --- ATA Learning Tap to hide [ ATA Learning ](/) * [Home](/) * [Tutorials](/tutorials/) * [Instructors](/author/) * [Advertising](/advertising/) * [Recommended Resources](/resources/) * [About Adam](/about-adam/) Search for: * [](https://twitter.com/adbertram) * [](https://github.com/Adam-the-Automator) * [](https://www.linkedin.com/company/adam-the-automator-llc) * [](/feed/) ![Robocopy /MIR: Sync Files with Ease and Confidence](https://adamtheautomator.com/wp-content/uploads/2020/08/Leveraging.png) # Robocopy /MIR: Sync Files with Ease and Confidence [![](https://secure.gravatar.com/avatar/f08b754bc0dce1c76685f6afa93185ecfb6f861fd14f993286e06bba69eaeb8b?s=192&d=mm&r=g)Adam Listek](https://adamtheautomator.com/author/alistek/)1 September 20206 min. read Categories: [IT Ops](/category/it-ops/) Tags:[Robocopy](/tag/robocopy/) Table of Contents * [What is so special about Robocopy /mir?](#h-what-is-so-special-about-robocopy-mir) * [File and Folder Security with the Mirror Command](#h-file-and-folder-security-with-the-mirror-command) * [Using Robocopy /mir in Practice](#h-using-robocopy-mir-in-practice) * [Mirror a Simple Directory to a Destination](#h-mirror-a-simple-directory-to-a-destination) * [Mirroring a Directory with Permissions](#h-mirroring-a-directory-with-permissions) * [Using the Mirror Command over the Network](#h-using-the-mirror-command-over-the-network) * [Conclusion](#h-conclusion) [Robocopy](https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/robocopy) is a top tool of system administrators around the world. Easily able to handle complex file transfer tasks, RoboCopy is a tried and true swiss army tool for any number of file transfer scenarios. Synchronizing files is a challenging problem for a myriad of reasons. The Robocopy /MIR switch aims to make the process of keeping two directories synchronized that much easier. Although this switch is not a two-way synchronization, there are many handy uses! > _If you want to learn more about robocopy, be sure to check out the [Ultimate Guide to Robocopy](https://adamtheautomator.com/robocopy/)!_ ## What is so special about Robocopy /mir? Let’s suppose that you have a temporary backup folder and you need to verify that all of the files in the source directory make it to a backup directory. Since backup files can get quite large, perhaps we want to make sure that the destination folder does not grow too quickly with stale backup files. Often manual backups or temporary copies are put into backup folders, and it is all too easy to run out of disk space. To make sure we don’t run out of storage space, the ideal transfer operation is a copy and purge. This operation makes sure that all of the files in the source directory make it to the destination directory and remove all destination files that are not present in the source directory. This type of scenario is exactly what the Robocopy /mir switch is made for! Functionally, Robocopy /mir is equivalent to the `/e /purge` options in Robocopy with a small difference in behavior. With the `/e /purge` options, a destination directories security settings are not overwritten. When using the `/mir` option, the security settings for the destination directory are overwritten. > `/mir` along with a handful of other commands are destructive to data if used incorrectly. This can potentially delete files in the destination directory so use with caution! ## File and Folder Security with the Mirror Command As mentioned above, there is a unique behavior related to security permissions and destination directories. When using the mirror switch, you might find that the file permissions themselves are not changed, only destination folder permissions. This is by design as for performance, and for practical reasons, individual file permissions were not intended to be copied using the mirror command. What does this look like in practice? Let’s take the example source directory folder structure like so: * **Folder1** * File1 – _Unique permissions_ * File2 * **Folder2** – _Unique permissions_ * File1 * File2 – _Unique permissions_ The result of a mirror command will result in the following file and folder permission structure. As you can see, the only permissions that are carried over are the unique folder permissions. The unique file permissions will not be carried over. * **Folder1** * File1 * File2 * **Folder2** – _Unique permissions_ * File1 * File1 * File2 Of course, there are plenty of scenarios where you would like the permissions to be copied and kept in sync; those scenarios will be explored in further detail later on in the article. ## Using Robocopy /mir in Practice There are many different ways to utilize the Robocopy /mir command, and certain behaviors have changed over time. These changes are primarily around copying file security permissions which are made easier in the Vista version of Robocopy. ### Mirror a Simple Directory to a Destination One of the simplest ways to take advantage of the mirror command is to simply mirror two directories on a single server. We will use two parameters, the Robocopy /mir command and the `/v` command for verbose logging and output. The verbose command is useful to see what Robocopy is doing and make sure the files that we want to copy are doing so. ```powershell robocopy D:\Articles\SourceDirectory\ D:\Articles\DestinationDirectory /mir /v ``` ![Mirror files from a source directory to a destination directory](https://adamtheautomator.com/wp-content/uploads/2020/08/Untitled-98.png) Mirror files from a source directory to a destination directory Depending on your needs, this might work just fine. File attributes are copied with the files, but the file security settings are not copied. The next example you may want to see is how to properly copy over the files with the security intact? ### Mirroring a Directory with Permissions To do a similar mirror operation but properly copy the file and folder permissions, we need to use the `/sec` and `/secfix` commands. The `/sec` command will copy the file security over for changed files, while the `/secfix` command will update the security for unchanged files. By combining these commands with `/mir` you will effectively mirror all of the files, folders, and permissions from a source directory to a destination. In this example, we have a directory with four files just like the first example. In addition, we have modified the permissions on _test2.txt_ to add an additional user with modify permissions. ![test2.txt security properties](https://adamtheautomator.com/wp-content/uploads/2020/08/Untitled-99.png) test2.txt security properties Here we are also going to modify _test3.txt_ in the destination folder with differing permissions to demonstrate how permissions will properly copy over utilizing the `/sec` and `/secfix` switches. ![test3.txt security properties](https://adamtheautomator.com/wp-content/uploads/2020/08/Untitled-100.png) test3.txt security properties After running the following command, we will see that the permissions related to the user are copied over. Since the files were the same but with different permissions, the correct permissions have been copied while the file data itself remains synced. > _Make sure to use [Run as Administrator](https://adamtheautomator.com/powershell-run-as-administrator/ "Run as Administrator") if you get access denied on copying over files. The setting of the permissions may require administrator rights to perform depending on your system security configuration._ ```powershell robocopy D:\Articles\SourceDirectory\ D:\Articles\DestinationDirectory /mir /sec /secfix /v ``` ![Mirror files from a source directory to a destination directory copying security settings as well](https://adamtheautomator.com/wp-content/uploads/2020/08/Untitled-2020-08-28T155204.524.png) Mirror files from a source directory to a destination directory copying security settings as well Looking at the _test2.txt_ file that had the source permissions changed, we will see that it copied over to the destination folder with the correct permissions. ![test2.txt security properties](https://adamtheautomator.com/wp-content/uploads/2020/08/Untitled-2020-08-28T155252.753.png) test2.txt security properties If we check on _test3.txt_ that had its destination directory permissions changed we will find that the file now has reverted to what the source directory permissions were. ![test3.txt security properties](https://adamtheautomator.com/wp-content/uploads/2020/08/Untitled-2020-08-28T155341.005.png) test3.txt security properties ## Using the Mirror Command over the Network This command works equally well over the network but to work to optimize the speed and performance, there are a [few extra commands](https://adamtheautomator.com/robocopy/) that can be very useful to use in conjunction with the `/mir` command. * `/zb` – Use restartable mode, and upon access denial, attempt to use the backup mode (shadow mode) * `/MT:nn` – Copy files using multiple threads, which you would define by replacing the `nn` placeholder with the number of threads. `8` is the default, and `16` is a reasonable number to test first. Keep in mind that more threads will need more CPU and memory to keep going. * `/tbd` – If you are transferring across network shares, then you may encounter Error 67 which is “network name cannot be found” and this option will attempt a retry on that error. * `/r:1 /w:3` – These two commands combined tell Robocopy to only retry once and wait 3 seconds in between. This value should be adjusted as necessary, perhaps 5-10 retries and 5 seconds in between, otherwise it will retry near indefinitely and 30 seconds in between. * `/fft` – Finally the FFT switch uses FAT file timing instead of NTFS which may introduce around a 2-second drift and less accuracy but more resiliency in transferring files. This is also important when transferring between file systems such as NTFS and EFS. * `/np` – This removes the progress bar indicator as this can become inaccurate with the multi-threaded nature of the transfer. > _On occasion the `/z` command can slow down performance, you may need to test with and without to maximize performance and reliability._ With all of these commands combined, you will have a robust solution for mirroring files over the network. To demonstrate this capability, we are mirroring files from a local directory to a remote file share using the fully qualified domain name (FQDN) of the remote server. Utilizing restartable backup mode, multi-threading, share error handling, FAT file timing, and optimized retry and wait times you should have a robust but performant solution to sending files over the network. ```powershell robocopy D:\Articles\SourceDirectory \\server1.fqdn\DestinationShare /mir /zb /mt:16 /tbd /r:1 /w:3 /fft /np ``` You may notice that in this example, we are not using the `/sec` or `/secfix` commands. The reason for this is dependant on your environment. If you are copying files between shares in the same domain then any permissions should properly transfer, unless they are unique local permissions. If you are transferring files between operating systems, or between shares in different domains or non-domain joined computers, then omitting these commands may work best. > _Adjust the multi-threading as necessary to find the proper balance between system performance, bandwidth allowance, and transfer speeds._ ## Conclusion System administrators often have complex file transfer needs. Despite many recent tools and solutions that have entered the scene, Robocopy /mir remains a popular solution. Built-in to Windows and updated continuously over new Windows releases, Robocopy remains a key tool when transferring files. Robocopy is a very powerful tool and specifically, the Robocopy /mir command allows for robust and useful file and folder mirroring across folders and network shares. With the addition of a few useful commands, Robocopy becomes even more powerful and reliable copying files over a network using the Robocopy /mir command. 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