frostfs-node/docs/evacuation.md

# Shard data evacuation

## Overview

Evacuation is the process of transferring data from one shard to another. Evacuation is used in case of problems with the shard in order to save data.

To start the evacuation, it is necessary that the shard is in read-only mode (read more [here](./shard-modes.md)).

First of all, by the evacuation the data is transferred to other shards of the same node; if it is not possible, then the data is transferred to other nodes.

Only one running evacuation process is allowed on the node at a time.

`frostfs-cli` utility is used to manage evacuation.

## Commands

`frostfs-cli control shards evacuation start` starts evacuation process for shards specified. To start evacuating all node shards, use the `--all` flag.

`frostfs-cli control shards evacuation stop` stops running evacuation process.

`frostfs-cli control shards evacuation status` prints evacuation process status.

See commands `--help` output for detailed description.

## Examples

### Set shard mode to read only
```bash
frostfs-cli control shards set-mode --mode read-only --endpoint s01.frostfs.devenv:8081 --wallet ./../frostfs-dev-env/services/storage/wallet01.json --id 8kEBwtvKLU3Hva3PaaodUi
Enter password >
Shard mode update request successfully sent.
```

### Start evacuation and get status
```bash
frostfs-cli control shards evacuation start --endpoint s01.frostfs.devenv:8081 --wallet ./../frostfs-dev-env/services/storage/wallet01.json --id 8kEBwtvKLU3Hva3PaaodUi
Enter password >
Shard evacuation has been successfully started.

frostfs-cli control shards evacuation status --endpoint s01.frostfs.devenv:8081 --wallet ./../frostfs-dev-env/services/storage/wallet01.json
Enter password >
Shard IDs: 8kEBwtvKLU3Hva3PaaodUi. Status: running. Evacuated 14 object out of 61, failed to evacuate 0 objects. Started at: 2023-05-10T10:13:06Z UTC. Duration: 00:00:03.

frostfs-cli control shards evacuation status --endpoint s01.frostfs.devenv:8081 --wallet ./../frostfs-dev-env/services/storage/wallet01.json
Enter password >
Shard IDs: 8kEBwtvKLU3Hva3PaaodUi. Status: running. Evacuated 23 object out of 61, failed to evacuate 0 objects. Started at: 2023-05-10T10:13:06Z UTC. Duration: 00:00:05.

frostfs-cli control shards evacuation status --endpoint s01.frostfs.devenv:8081 --wallet ./../frostfs-dev-env/services/storage/wallet01.json
Enter password >
Shard IDs: 8kEBwtvKLU3Hva3PaaodUi. Status: completed. Evacuated 61 object out of 61, failed to evacuate 0 objects. Started at: 2023-05-10T10:13:06Z UTC. Duration: 00:00:13.
```

### Stop running evacuation process
```bash
frostfs-cli control shards evacuation start --endpoint s01.frostfs.devenv:8081 --wallet ./../frostfs-dev-env/services/storage/wallet01.json --id 54Y8aot9uc7BSadw2XtYr3
Enter password >
Shard evacuation has been successfully started.

frostfs-cli control shards evacuation status --endpoint s01.frostfs.devenv:8081 --wallet ./../frostfs-dev-env/services/storage/wallet01.json
Enter password >
Shard IDs: 54Y8aot9uc7BSadw2XtYr3. Status: running. Evacuated 15 object out of 73, failed to evacuate 0 objects. Started at: 2023-05-10T10:15:47Z UTC. Duration: 00:00:03.

frostfs-cli control shards evacuation stop --endpoint s01.frostfs.devenv:8081 --wallet ./../frostfs-dev-env/services/storage/wallet01.json
Enter password >
Evacuation stopped.

frostfs-cli control shards evacuation status --endpoint s01.frostfs.devenv:8081 --wallet ./../frostfs-dev-env/services/storage/wallet01.json
Enter password >
Shard IDs: 54Y8aot9uc7BSadw2XtYr3. Status: completed. Evacuated 31 object out of 73, failed to evacuate 0 objects. Error: context canceled. Started at: 2023-05-10T10:15:47Z UTC. Duration: 00:00:07.
```

### Start evacuation and await it completes
```bash
frostfs-cli control shards evacuation start --endpoint s01.frostfs.devenv:8081 --wallet ./../frostfs-dev-env/services/storage/wallet01.json --id 54Y8aot9uc7BSadw2XtYr3 --await
Enter password >
Shard evacuation has been successfully started.
Progress will be reported every 5 seconds.
Shard IDs: 54Y8aot9uc7BSadw2XtYr3. Status: running. Evacuated 18 object out of 73, failed to evacuate 0 objects. Started at: 2023-05-10T10:18:42Z UTC. Duration: 00:00:04.
Shard IDs: 54Y8aot9uc7BSadw2XtYr3. Status: running. Evacuated 43 object out of 73, failed to evacuate 0 objects. Started at: 2023-05-10T10:18:42Z UTC. Duration: 00:00:09.
Shard IDs: 54Y8aot9uc7BSadw2XtYr3. Status: running. Evacuated 68 object out of 73, failed to evacuate 0 objects. Started at: 2023-05-10T10:18:42Z UTC. Duration: 00:00:14.
Shard evacuation has been completed.
Shard IDs: 54Y8aot9uc7BSadw2XtYr3. Evacuated 73 object out of 73, failed to evacuate 0 objects. Started at: 2023-05-10T10:18:42Z UTC. Duration: 00:00:14.
```

### Start evacuation and await it completes without progress notifications
```bash
frostfs-cli control shards evacuation start --endpoint s01.frostfs.devenv:8081 --wallet ./../frostfs-dev-env/services/storage/wallet01.json --id 54Y8aot9uc7BSadw2XtYr3 --await --no-progress
Enter password > 
Shard evacuation has been successfully started.
Shard evacuation has been completed.
Shard IDs: 54Y8aot9uc7BSadw2XtYr3. Evacuated 73 object out of 73, failed to evacuate 0 objects. Started at: 2023-05-10T10:20:00Z UTC. Duration: 00:00:14.
```