---
#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**, ideally within a `tmux` session
   * 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: /usr/local/bin/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: /meg)
  -S | --space-source SPACE          Source project space name (default: data1)
  -B | --experiment-dst-basedir DIR  Experiment base directory (default: /data/project/meg)
  -D | --space-destination SPACE     Destination project space name (default: data1)
  -p | --project-name PRJ_NAME       Mantadory field. MeG project name. Examples:
                                     - 'online'
                                     - 'offline'
                                     - 'shared'
  -F | --force-destination-mkdir     Create the destination parent directory (default: false)
                                     Example: mkdir -p $(dirname /data/project/meg/data1/PROJECT_NAME)
                                     Result:  mkdir -p /data/project/meg/data1
  -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 examples

##### Example: Migrating the Entire `online` Directory

The following example demonstrates how to migrate the **entire `online`** directory.

{{site.data.alerts.tip}}
You may also choose to migrate only specific subdirectories if needed.
However, migrating full directories is generally <b>simpler</b> and <b>less error-prone</b> compared to handling multiple subdirectory migrations.
{{site.data.alerts.end}}

```bash
[root@meg-s-001 ~]# experiment_migration.bash -S data1 -D data1 -p "online"
🔄 Transferring project:
   From: /meg/data1/online
   To:   login001.merlin7.psi.ch:/data/project/meg/data1/online
   Threads: 10 | Split: 20000 files | Max size: 100G
   RunID: 

Please confirm to start (y/N): 
❌ Transfer cancelled by user.
```

##### Example: Migrating a Specific Subdirectory

The following example demonstrates how to migrate **only a subdirectory**. In this case, we use the option `-F` to create the parent directory in the destination, to ensure that this exists before transferring:

⚠️ **Important:**  
- When migrating a subdirectory, **do not** run concurrent migrations on its parent directories.
- For example, avoid running migrations with `-p "shared"` while simultaneously migrating `-p "shared/subprojects"`.

```bash
[root@meg-s-001 ~]#  experiment_migration.bash -p "shared/subprojects/meg1" -F
🔄 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
❌ Transfer cancelled by user.
```

This command initiates the migration of the directory, by creating the destination parant directory (`-F` option): 
* Creates the destination directory as follows:

  ```bash
  ssh login002.merlin.psi.ch mkdir -p /data/project/meg/data1/shared/subprojects
  ```
* Runs FPSYNC with 10 threads and N parts of max 20000 files or 100G files:
  * Source: `/meg/data1/shared/subprojects/meg1` 
  * Destination: `login002.merlin7.psi.ch:/data/project/meg/data1/shared/subprojects/meg1`