persist data with a citus cluster

I'm pretty new to Citus so be easy on me ;)

The documentation mentions that the citus_standalone is storing the PGDATA in a mounted volume (,so it persist between restarts of the container)

I am trying to start the citus cluster with data persistency. Do I have to do something for this?

First of all I had to change the docker-compose.yml file a little bit.
I'm running ```docker-compose version 1.17.0, build ac53b73```

```
version: '2.3'

services:

master:
container_name: "${COMPOSE_PROJECT_NAME:-citus}_master"
image: citusdata/citus:7.1.1
ports:
- "5432:5432"
labels:
com.citusdata.role: Master

worker:
container_name: "${COMPOSE_PROJECT_NAME:-citus}_worker"
image: citusdata/citus:7.1.1
labels:
com.citusdata.role: Worker
depends_on: { manager: { condition: service_healthy } }
manager:
container_name: "${COMPOSE_PROJECT_NAME:-citus}_manager"
image: 'citusdata/membership-manager:0.2.0'
volumes: ['/var/run/docker.sock:/var/run/docker.sock']
depends_on: { master: { condition: service_healthy } }
```

I created two directories on my host environment to store the pgdata for the Master and the Worker
The docker-compose files looks now like:
```
version: '2.3'

services:
master:
container_name: "${COMPOSE_PROJECT_NAME:-citus}_master"
image: citusdata/citus:7.1.1
ports:
- "5432:5432"
labels:
com.citusdata.role: Master
volumes:
- /media/marco/DataDisk/citus-master:/var/lib/postgresql/data

worker:
container_name: "${COMPOSE_PROJECT_NAME:-citus}_worker"
image: citusdata/citus:7.1.1
labels:
com.citusdata.role: Worker
volumes:
- /media/marco/DataDisk/citus-worker:/var/lib/postgresql/data
depends_on: { manager: { condition: service_healthy } }
manager:
container_name: "${COMPOSE_PROJECT_NAME:-citus}_manager"
image: 'citusdata/membership-manager:0.2.0'
volumes: ['/var/run/docker.sock:/var/run/docker.sock']
depends_on: { master: { condition: service_healthy } }

```

```docker-compose up``` works fine. And I can create a database etc.

However after a ```docker-compose down```
and then a new start ```docker-compose up``` , it has the tables but it cannot find the shards.

```
ERRO[2017-12-11T04:31:45Z] pq: could not find length of shard 102072 req_id=ZXvdeL1Mh2-1
```

I'm pretty new here. So not sure what is going on?
- Can I define my own volumes?
- Should I do an 'up' and 'down' or only 'start' 'stop'
- Where is the shared information persisted?

Thanks for any help

Marco