Move a volume

A volume lives on one server. With Ployz Cloud you can keep a read-only copy of it on a second server, called a mirror, and move the volume and the service that mounts it to another server. Without Cloud, volumes stay on the server that has them.

Mirror a volume

A mirror holds the volume's data as of its last sync. It refreshes only when you sync it, and a volume has at most one.

ployz volume mirror data --to web-2     # copy data to web-2; it shows as data-web-2
ployz volume sync data                   # send what changed since the last sync
ployz volume mirror rm data-web-2        # delete the mirror
ployz volume runs data                   # what ran on this volume, and how it ended

Each command starts a run in Ployz Cloud and prints its id. Add --wait to wait for it to finish. One run at a time per volume: a second one is refused and names the run in progress.

Move a volume to another server

ployz volume move data --to web-2

Your service keeps running while Ployz copies the volume and its image to web-2. Then Ployz stops the service, sends what changed during the copy, and starts the service on web-2 with the same volume. Your service is down only for that last step. A service that takes a while to stop or start doesn't fail the move: Ployz waits for Docker, up to ten minutes for each stop or start.

The old server keeps a read-only copy, shown as data-web-1. Moving back sends only what changed since. If the volume already has a mirror on web-2, the move starts from it. From the moment the service stops until the move ends, deploys of it are refused.

When a move stops

A move can stop if a server or Ployz Cloud goes away during it. ployz volume runs data shows why. What happens next depends on how far it got.

Before the handover, Ployz starts your service again on the old server, with all its data. The run fails and names what went wrong. Run the move again when you're ready.
After the handover, the volume belongs to the new server, and your service stays down until the move finishes there. The run says so: volume move data --to web-2 again continues from there. Run that line; it picks up where the move stopped.

If the move stopped and nothing started your service again, release the volume:

ployz volume release data

Release starts the service again on the old server. It's refused once the volume has been handed over, and names the move to run instead.

Good to know

A server must answer for its volume to move. If the volume's server is down, neither a move nor a release can run, and the run says which server did not answer. See When its server goes down.
A mirror is not a backup. It holds the data as of its last sync, on one of your servers. Keep your own copies off your servers; see Back up a database.
A mirror that fell behind for good is refused with data-web-2 diverged. Run ployz volume sync data --full to copy everything again.
Deleting a volume deletes its mirror. So does deleting its environment. A mirror that is the volume's only copy left is removed only with --confirm data, because its data goes with it.