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Updated How to enable VSS for rclone (markdown)
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**The goal of this wiki to show you how easy it is to enable VSS for rclone or any windows app.**
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***
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**Background**
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As per [Wikipedia](https://en.wikipedia.org/wiki/Shadow_Copy):
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> Volume Snapshot Service or VSS is a technology included in Microsoft Windows that can create backup copies or snapshots of computer files or volumes, even when they are in use. A snapshot is a read-only point-in-time copy of the volume. Snapshots allow the creation of consistent backups of a volume, ensuring that the contents do not change and are not locked while the backup is being made.
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***
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**Use case**
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I use rclone to copy very large files created by Veeam Backup and Replication which can take 24+ hours, depending on the size of the files and internet speeds.
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If Veeam backup software would run again while rclone is still uploading, Veeam would modify the set of files that rclone is still uploading, resulting in a corrupted and uselss set of backup files. Or if I wanted rclone to check a set of large sized files, Veeam might run again and modify the local files while rclone is still checking and generate errors in the log files.
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So I create a VSS read-only point-in-time snapshot and have rclone use that as the source.
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Now rclone can takes its time, upload, sync, check or whatever and not be concerned that the data will be modified.
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--- The snapshot's files are never in-use. rclone will not get an error about in-use files.
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--- The snapshot's files are never locked. rclone will not get an error about locked files.
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Now rclone can takes its time, upload, sync, check or whatever and not be concerned that the data will be modified:
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- The snapshot's files are never in-use. rclone will not get an error about in-use files.
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- The snapshot's files are never locked. rclone will not get an error about locked files.
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***
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**How to**
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Let's say that we want to sync c:\data\ to the cloud.
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Let's say that we want to sync `c:\data\` to the cloud.
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1 - Create a file named vs.cmd:
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1 - Create a file named `vs.cmd`:
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vshadow.exe -nw -script=setvars.cmd -exec=exec.cmd c:
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2 - Create a file named exec.cmd file:
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2 - Create a file named `exec.cmd` file:
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rem Load the the variables created by vshadow.exe
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call setvars.cmd
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rem Create the symbolic link to the snapshot
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rem Create the symbolic link to the snapshot (the backslash after shadow_device_1 is important!)
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mklink /d c:\snapshot\ %shadow_device_1%\
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rem Execute rclone with the source as c:\snapshot\data\, not c:\data\
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rclone sync c:\snapshot\data\ dest:data
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rem Delete the symbolic link
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rmdir c:\snapshot\ /q
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rmdir c:\snapshot\
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That is all it takes to create a shadow mount.
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When vs.cmd is run, it will execute vshadow.exe.
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To run the sync execute `vs.cmd` (1), which will:
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1. Execute `vshadow.exe`, which will:
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1. Create the snapshot
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2. Create a file named `setvars.cmd` with some variables identifying the snapshot created
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3. Execute `exec.cmd`, which will:
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1. Load variables from `setvars.cmd`
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2. Mount the snapshot identified by the variables
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3. Execute the rclone command to sync from the snapshot
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4. Unmount the snapshot
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4. Delete the snapshot
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vshadow.exe will:
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1. Create a file named setvars.cmd with some variables that needs to be passed to exec.cmd.
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2. Create the snapshot.
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3. Execute exec.cmd.
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Note that c:\snapshot\ is a temporaty symbolc link only accessible while exec.cmd is running. when exec.cmd exits, the snapshot is removed by Windows operating system.
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Note:
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- The `vs.cmd` must be run with administrator privileges.
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- The path `c:\snapshot\` is a temporary symbolic link only accessible while exec.cmd is running.
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- The contents of `c:\snapshot\` that rclone sees, is a mirror image of `c:\`, meaning there will be a directory `c:\snapshot\Program Files` mirroring `c:\Program Files` etc.
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- When exec.cmd exits, the snapshot is removed by Windows operating system.
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***
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**Variants**
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I find it confusing, that c:\snapshot\ is a mirror image of c:\\
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It may be confusing that `c:\snapshot\` is a mirror image of `c:\`, and when writing more complex scripts this confusion may easily lead to bugs. Here are some alternative variants of `exec.cmd` that could make it clearer.
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1 - Use SUBST command to make an alias of `c:`
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When I was writing more complex scripts, this confusion was leading to bugs.
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So I will give you 3 workarounds for clearer code for exec.cmd.
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(a) You may find it less confusing if you create an alias `t:` that you can use when referrring to the snapshot:
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```
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call setvars.cmd
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mklink /d c:\snapshot\ %shadow_device_1%\
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subst t: c:\
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rclone sync t:\snapshot\data\ dest:data
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subst t: /d
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rmdir c:\snapshot\
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```
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--- Use SUBST command.
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(b) Alternatively, instead of just making `t:` an alias to the entire `c:` drive, you can make it an alias directly into the snapshot image at `c:\snapshot\`. Then the paths on `c:` you would normally use with rclone directly without vss, now becomes identical when used on the snapshot `t:`. This has the additional benefit of not increasing the path lengths of the source paths that rclone gets to work with, in case that could hit some limit.
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```
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call setvars.cmd
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mklink /d c:\snapshot\ %shadow_device_1%\
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subst t:\data\ c:\snapshot\
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rclone sync t:\ dest:data
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subst t: /d
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rmdir c:\snapshot\
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```
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call setvars.cmd
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mklink /d c:\snapshot\ %shadow_device_1%\
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subst t: c:\
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rclone sync t:\snapshot\data\ dest:data
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subst t: /d
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rmdir c:\snapshot\ /q
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2 - Use NET USE command
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```
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call setvars.cmd
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mklink /d c:\snapshot\ %shadow_device_1%\
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net share snapshot=c:\
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rclone sync \\localhost\snapshot\data\ dest:data
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net share snapshot /delete
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rmdir c:\snapshot\
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```
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--- Use NET USE command
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call setvars.cmd
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mklink /d c:\snapshot\ %shadow_device_1%\
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net share snapshot=c:\
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rclone sync \\localhost\snapshot\data\ dest:data
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net share snapshot /delete
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rmdir c:\snapshot\ /q
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--- Create a new drive letter.
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3 - Create a new drive letter
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This is what I do as this is the most reliable and least code needed.
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Create a new drive and use that for the mount point.
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Most computers will not have free space to create a new drive. So shrink your c: drive by just 1MB and use that space to create new partition and name it the b: drive. Since the b: drive will only be used to mount the vss point, 1MB is plenty of space.
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call setvars.cmd
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mklink /d b:\snapshot\ %shadow_device_1%\
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rclone sync b:\snapshot\data\ dest:data
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rmdir b:\snapshot\ /q
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```
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call setvars.cmd
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mklink /d b:\snapshot\ %shadow_device_1%\
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rclone sync b:\snapshot\data\ dest:data
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rmdir b:\snapshot\
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```
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Good luck and if you have any questions or comments, please do not hesitate to contact me.
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Create a post at the forum and put the "VSS question" in the subject and I will answer.
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***
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**Details**
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Now for the boring details.
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