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---
#tags:
keywords: meg, merlin6, merlin7, migration, fpsync, rsync
#summary: ""
sidebar: meg_sidebar
last_updated: 28 May 2025
permalink: /meg/migrating.html
---
# Meg to Merlin7 Migration Guide
Welcome to the official documentation for migrating experiment data from **MEG** to **Merlin7**. Please follow the instructions carefully to ensure a smooth and secure transition.
---
## Directory Structure Changes
### Meg vs Merlin6 vs Merlin7
| Cluster | Home Directory | User Data Directory | Experiment data | Additional notes |
| ------- | :----------------- | :------------------ | --------------------- | ---------------- |
| merlin6 | /psi/home/`$USER` | /data/user/`$USER` | /data/experiments/meg | Symlink /meg |
| meg | /meg/home/`$USER` | N/A | /meg | |
| merlin7 | /data/user/`$USER` | /data/user/`$USER` | /data/project/meg | |
* The **Merlin6 home and user data directores have been merged** into the single new home directory `/data/user/$USER` on Merlin7.
* This is the same for the home directory in the meg cluster, which has to be merged into `/data/user/$USER` on Merlin7.
* Users are responsible for moving the data.
* The **experiment directory has been integrated into `/data/project/meg`**.
### Recommended Cleanup Actions
* Remove unused files and datasets.
* Archive large, inactive data sets.
### Mandatory Actions
* Stop activity on Meg and Merlin6 when performing the last rsync.
## Migration Instructions
### Preparation
A `experiment_migration.setup` migration script must be executed from **any MeG node** using the account that will perform the migration.
#### When using the local `root` account
- The script **must be executed after every reboot** of the destination nodes.
- **Reason:** On Merlin7, the home directory for the `root` user resides on ephemeral storage (no physical disk).
After a reboot, this directory is cleaned, so **SSH keys need to be redeployed** before running the migration again.
#### When using a PSI Active Directory (AD) account
- Applicable accounts include, for example:
- `gac-meg2_data`
- `gac-meg2`
- The script only needs to be executed **once**, provided that:
- The home directory for the AD account is located on a shared storage area.
- This shared storage is accessible from the node executing the transfer.
- **Reason:** On Merlin7, these accounts have their home directories on persistent shared storage, so the SSH keys remain available across reboots.
To run it:
```bash
experiment_migration.setup
```
This script will:
* Check that you have an account on Merlin7.
* Configure and check that your environment is ready for transferring files via Slurm job.
If there are issues, the script will:
* Print clear diagnostic output
* Give you some hints to resolve the issue
If you are stuck, email: [merlin-admins@lists.psi.ch](mailto:merlin-admins@lists.psi.ch)/[meg-admins@lists.psi.ch](mailto:meg-admins@lists.psi.ch)
### Migration Procedure
1. **Run an initial sync**
* This copies the bulk of the data from MeG to Merlin7.
* **IMPORTANT: Do not modify the destination directories**
* Please, before starting the transfer ensure that:
* The source and destination directories are correct.
* The destination directories exist.
2. **Run additional syncs if needed**
* Subsequent syncs can be executed to transfer changes.
* Ensure that **only one sync for the same directory runs at a time**.
* Multiple syncs are often required since the first one may take several hours or even days.
3. Schedule a date for the final migration:
* Any activity must be stopped on the source directory.
* In the same way, no activity must be done on the destination until the migration is complete.
4. **Perform a final sync with the `-E` option** (if it applies)
* Use `-E` **only if you need to delete files on the destination that were removed from the source.**
* This ensures the destination becomes an exact mirror of the source.
* **Never use `-E` after the destination has gone into production**, as it will delete new data created there.
5. Disable access on the source folder.
6. Enable access on the destination folder.
* At this point, **no new syncs have to be performed.**
> ⚠️ **Important Notes**
> The `-E` option is destructive; handle with care.
> Always verify that the destination is ready before triggering the final sync.
> For optimal performance, use up to 12 threads with the -t option.
#### Running The Migration Script
The migration script is installed on the `meg-s-001` server at:
`/usr/local/bin/experiment_migration.bash`
This script is primarily a **wrapper** around `fpsync`, providing additional logic for synchronizing MeG experiment data.
```bash
[root@meg-s-001 ~]# experiment_migration.bash --help
Usage: ./experiment_migration.bash [options] -p <project_name>
Options:
-t | --threads N Number of parallel threads (default: 10). Recommended 12 as max.
-b | --experiment-src-basedir DIR Experiment base directory (default: /data/experiment/meg)
-B | --experiment-dst-basedir DIR Experiment base directory (default: /data/experiment/meg)
-S | --space-source SPACE Source project space name (default: data1)
-D | --space-destination SPACE Destination project space name (default: data1)
-p | --project-name PRJ_NAME Mantadory field. MeG project name. Examples:
- 'online'
- 'offline'
- 'shared'
-s | --split N Number of files per split (default: 20000)
-f | --filesize SIZE File size threshold (default: 100G)
-r | --runid ID Reuse an existing runid session
-l | --list-runids List available runid sessions and exit
-x | --delete-runid Delete runid. Requires: -r | --runid ID
-E | --rsync-delete-option [WARNING] Use this to delete files in the destination
which are not present in the source any more.
[WARNING] USE THIS OPTION CAREFULLY!
Typically used in last rsync to have an exact
mirror of the source directory.
[WARNING] Some files in destination might be deleted!
Use 'man fpsync' for more information.
-h | --help Show this help message
-v | --verbose Run fpsync with -v option
```
> Defaults can be updated if necessary.
#### Migration example
The following example migrates the entire online data
```bash
[root@meg-s-001 bin]# experiment_migration.bash -b /meg -S /data/project/meg -S data1 -D data1 -p "online"
🔄 Transferring project:
From: /meg/data1/online
To: login002.merlin7.psi.ch:/data/experiment/meg/data1/online
Threads: 10 | Split: 20000 files | Max size: 100G
RunID:
Please confirm to start (y/N): N
❌ Transfer cancelled by user.
```
The following example migrates a subdirectory:
```bash
[root@meg-s-001 bin]# experiment_migration.bash -b /meg -B /data/project/meg -S data1 -D data1 -p "shared/subprojects/meg1"
🔄 Transferring project:
From: /meg/data1/shared/subprojects/meg1
To: login002.merlin7.psi.ch:/data/project/meg/data1/shared/subprojects/meg1
Threads: 10 | Split: 20000 files | Max size: 100G
RunID:
Please confirm to start (y/N): N
```