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---
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#tags:
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keywords: meg, merlin6, merlin7, migration, fpsync, rsync
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#summary: ""
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sidebar: meg_sidebar
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last_updated: 28 May 2025
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permalink: /meg/migrating.html
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---
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# Meg to Merlin7 Migration Guide
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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.
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---
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## Directory Structure Changes
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### Meg vs Merlin6 vs Merlin7
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| Cluster | Home Directory | User Data Directory | Experiment data | Additional notes |
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| ------- | :----------------- | :------------------ | --------------------- | ---------------- |
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| merlin6 | /psi/home/`$USER` | /data/user/`$USER` | /data/experiments/meg | Symlink /meg |
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| meg | /meg/home/`$USER` | N/A | /meg | |
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| merlin7 | /data/user/`$USER` | /data/user/`$USER` | /data/project/meg | |
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* The **Merlin6 home and user data directores have been merged** into the single new home directory `/data/user/$USER` on Merlin7.
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* This is the same for the home directory in the meg cluster, which has to be merged into `/data/user/$USER` on Merlin7.
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* Users are responsible for moving the data.
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* The **experiment directory has been integrated into `/data/project/meg`**.
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### Recommended Cleanup Actions
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* Remove unused files and datasets.
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* Archive large, inactive data sets.
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### Mandatory Actions
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* Stop activity on Meg and Merlin6 when performing the last rsync.
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## Migration Instructions
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### Preparation
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A `experiment_migration.setup` migration script must be executed from **any MeG node** using the account that will perform the migration.
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#### When using the local `root` account
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- The script **must be executed after every reboot** of the destination nodes.
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- **Reason:** On Merlin7, the home directory for the `root` user resides on ephemeral storage (no physical disk).
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After a reboot, this directory is cleaned, so **SSH keys need to be redeployed** before running the migration again.
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#### When using a PSI Active Directory (AD) account
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- Applicable accounts include, for example:
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- `gac-meg2_data`
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- `gac-meg2`
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- The script only needs to be executed **once**, provided that:
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- The home directory for the AD account is located on a shared storage area.
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- This shared storage is accessible from the node executing the transfer.
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- **Reason:** On Merlin7, these accounts have their home directories on persistent shared storage, so the SSH keys remain available across reboots.
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To run it:
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```bash
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experiment_migration.setup
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```
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This script will:
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* Check that you have an account on Merlin7.
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* Configure and check that your environment is ready for transferring files via Slurm job.
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If there are issues, the script will:
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* Print clear diagnostic output
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* Give you some hints to resolve the issue
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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)
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### Migration Procedure
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1. **Run an initial sync**, ideally within a `tmux` session
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* This copies the bulk of the data from MeG to Merlin7.
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* **IMPORTANT: Do not modify the destination directories**
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* Please, before starting the transfer ensure that:
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* The source and destination directories are correct.
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* The destination directories exist.
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2. **Run additional syncs if needed**
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* Subsequent syncs can be executed to transfer changes.
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* Ensure that **only one sync for the same directory runs at a time**.
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* Multiple syncs are often required since the first one may take several hours or even days.
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3. Schedule a date for the final migration:
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* Any activity must be stopped on the source directory.
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* In the same way, no activity must be done on the destination until the migration is complete.
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4. **Perform a final sync with the `-E` option** (if it applies)
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* Use `-E` **only if you need to delete files on the destination that were removed from the source.**
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* This ensures the destination becomes an exact mirror of the source.
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* **Never use `-E` after the destination has gone into production**, as it will delete new data created there.
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5. Disable access on the source folder.
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6. Enable access on the destination folder.
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* At this point, **no new syncs have to be performed.**
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> ⚠️ **Important Notes**
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> The `-E` option is destructive; handle with care.
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> Always verify that the destination is ready before triggering the final sync.
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> For optimal performance, use up to 12 threads with the -t option.
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#### Running The Migration Script
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The migration script is installed on the `meg-s-001` server at:
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`/usr/local/bin/experiment_migration.bash`
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This script is primarily a **wrapper** around `fpsync`, providing additional logic for synchronizing MeG experiment data.
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```bash
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[root@meg-s-001 ~]# experiment_migration.bash --help
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Usage: /usr/local/bin/experiment_migration.bash [options] -p <project_name>
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Options:
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-t | --threads N Number of parallel threads (default: 10). Recommended 12 as max.
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-b | --experiment-src-basedir DIR Experiment base directory (default: /meg)
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-S | --space-source SPACE Source project space name (default: data1)
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-B | --experiment-dst-basedir DIR Experiment base directory (default: /data/project/meg)
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-D | --space-destination SPACE Destination project space name (default: data1)
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-p | --project-name PRJ_NAME Mantadory field. MeG project name. Examples:
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- 'online'
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- 'offline'
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- 'shared'
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-F | --force-destination-mkdir Create the destination parent directory (default: false)
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Example: mkdir -p $(dirname /data/project/meg/data1/PROJECT_NAME)
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Result: mkdir -p /data/project/meg/data1
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-s | --split N Number of files per split (default: 20000)
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-f | --filesize SIZE File size threshold (default: 100G)
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-r | --runid ID Reuse an existing runid session
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-l | --list-runids List available runid sessions and exit
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-x | --delete-runid Delete runid. Requires: -r | --runid ID
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-E | --rsync-delete-option [WARNING] Use this to delete files in the destination
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which are not present in the source any more.
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[WARNING] USE THIS OPTION CAREFULLY!
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Typically used in last rsync to have an exact
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mirror of the source directory.
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[WARNING] Some files in destination might be deleted!
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Use 'man fpsync' for more information.
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-h | --help Show this help message
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-v | --verbose Run fpsync with -v option
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```
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> Defaults can be updated if necessary.
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#### Migration examples
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##### Example: Migrating the Entire `online` Directory
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The following example demonstrates how to migrate the **entire `online`** directory.
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{{site.data.alerts.tip}}
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You may also choose to migrate only specific subdirectories if needed.
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However, migrating full directories is generally <b>simpler</b> and <b>less error-prone</b> compared to handling multiple subdirectory migrations.
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{{site.data.alerts.end}}
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```bash
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[root@meg-s-001 ~]# experiment_migration.bash -S data1 -D data1 -p "online"
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🔄 Transferring project:
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From: /meg/data1/online
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To: login001.merlin7.psi.ch:/data/project/meg/data1/online
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Threads: 10 | Split: 20000 files | Max size: 100G
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RunID:
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Please confirm to start (y/N):
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❌ Transfer cancelled by user.
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```
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##### Example: Migrating a Specific Subdirectory
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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:
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⚠️ **Important:**
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- When migrating a subdirectory, **do not** run concurrent migrations on its parent directories.
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- For example, avoid running migrations with `-p "shared"` while simultaneously migrating `-p "shared/subprojects"`.
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```bash
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[root@meg-s-001 ~]# experiment_migration.bash -p "shared/subprojects/meg1" -F
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🔄 Transferring project:
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From: /meg/data1/shared/subprojects/meg1
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To: login002.merlin7.psi.ch:/data/project/meg/data1/shared/subprojects/meg1
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Threads: 10 | Split: 20000 files | Max size: 100G
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RunID:
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Please confirm to start (y/N): N
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❌ Transfer cancelled by user.
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```
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This command initiates the migration of the directory, by creating the destination parant directory (`-F` option):
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* Creates the destination directory as follows:
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```bash
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ssh login002.merlin.psi.ch mkdir -p /data/project/meg/data1/shared/subprojects
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```
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* Runs FPSYNC with 10 threads and N parts of max 20000 files or 100G files:
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* Source: `/meg/data1/shared/subprojects/meg1`
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* Destination: `login002.merlin7.psi.ch:/data/project/meg/data1/shared/subprojects/meg1`
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