Mirror a volume

A mirror is a read-only copy of a volume on a second server. Ployz Cloud refreshes it on every deploy and every 15 minutes. It keeps a backup of your data on your own servers, lets you move the volume there, and gives the volume a restore point.

A volume has one mirror for now. Every server with storage needs a newer Ployz before a volume can have one. Until then the volume's Copies only shows, and names the servers to upgrade, for example "Upgrade db-1 to a newer Ployz". The 15-minute refresh waits too.

Add a mirror

1. Open a managed volume after its first deploy and go to Copies.
2. Under Elsewhere, click Add copy and choose a server. It offers only servers that run services.
3. Click Deploy.

Until you deploy, the new mirror shows in green and counts in the bottom bar and Details, where you can discard it. Details reads "Seed" for it. The deploy copies the volume before it starts your services.

Check on a mirror

Copies lists where the volume's data lives. Live is the server your service writes on. Elsewhere holds the mirror and any old copy a move left, each with when it last refreshed.

On the canvas the mirror hangs under its volume's tray as its own small card, for example data-web-2 with "Mirror · 4 minutes ago". A mirror more than an hour behind shows its age in amber with a warning sign. A staged mirror shows New in green, a staged removal shows Removing in red, and a mirror about to become the primary shows Primary in pink.

Click a mirror, on the canvas or under Elsewhere, to open it. It shows its server, when it last refreshed, Refresh now, Make primary and Remove mirror. A mirror more than an hour behind says Refresh skipped and why. Either its server is not answering or its last refresh failed. It also says how much of its writes a failover would lose.

A mirror stays listed while its server is not answering. A mirror made with ployz volume mirror is then known only from that server's last report, so its row reads "Last reported", with no age. It may have been removed since. Copies can't make it primary, remove it or refresh it until its server answers. If Copies knows of no copy outside web-1 while another server hasn't reported, Elsewhere says why, for example "web-2 is not answering, so Copies can't say what is outside web-1".

Refresh a mirror

Click Refresh now on the mirror. It sends the mirror what changed since its last refresh and answers at once, for example "data-web-2 is pulling w-3-1760340000". The mirror reads "Refreshing" while it downloads, and its age resets when the download lands.

If a move or release is running on the volume, Refresh now says so instead, since a move's own copy refreshes the mirror. A download that fails is reported once, with its server's reason, and the mirror shows the failure until a later refresh lands.

Remove a mirror

1. Click the mirror and click Remove mirror. It shows in red until you deploy.
2. Click Deploy. Type your project/environment, like my-app/production, and click Deploy. The deploy asks because the mirror's data goes with it.

Details reads "Delete" for the removal. A staged mirror has no Make primary or Remove mirror, and a new one has no Refresh now. To undo a staged change, discard it in Details. See Confirm a deploy that deletes data.

Mirror from the CLI

The CLI runs each of these at once, without waiting for a deploy:

ployz volume mirror data --to web-2     # copy data to web-2; it shows as data-web-2
ployz volume sync data                   # send the mirror what changed since its last refresh
ployz volume sync data --full            # copy everything again
ployz volume mirror rm data-web-2        # delete the mirror

ployz volume sync without --full works like Refresh now and prints what it did. If a server doesn't answer in time, the sync says the server may still have taken it. Run ployz volume sync data again to see where each mirror got to. Copying a big volume, for a mirror or a move, can take hours. If a copy hasn't finished after six hours, the run fails and says so.

ployz volume mirror rm deletes the copy on that server, whether it's the mirror or an old copy. Add --if-old-copy to delete it only while it is still an old copy. Every cleanup line Ployz prints for an old copy includes it. A mirror that is the volume's only copy left is removed only with --confirm data, because its data goes with it.

In a Protected environment, ployz volume mirror rm from a member, or from a token or an agent without environments:protect, waits for an owner or admin to approve it. Adding a mirror and syncing don't ask.

Good to know

• A mirror isn't an offsite backup. It holds the data as of its last refresh, on another of your servers. For a copy off your servers, see Back up a database.
• A mirror that fell behind for good gets a full copy. When the volume's server no longer holds any point the mirror has, the next refresh or move sends the whole volume.
• Deleting a volume deletes its mirror. So does deleting its environment.