Docker metrics
The Docker group is Docker's own accounting of its data root: layers, images, containers, volumes, and build cache, each with the share a prune would free. It is read from the Engine's disk-usage report every five minutes on the daemon's own timer, never on the sample tick, and the whole breakdown sums to the Docker total on Storage usage.
Granted from S2
On TurboPanel High Availability this family is part of the S2 and higher entitlement. An S1 server still shows the Docker data-root total under Storage usage; in place of this group the console shows a one-line notice saying the tier does not include it. Self-hosted and seats with no tier assigned keep the group. See License tiers.
A host with no Docker socket, or whose Engine is unhealthy this minute, reports nothing — absent, not zero.
Image layers
| Series | Wire name | What it is |
|---|---|---|
| Layers | dockerUsage.layersBytes | Bytes in image layers on disk |
| Reclaimable (dangling) | dockerUsage.imagesReclaimableBytes | Bytes in images no container references — what an image prune frees |
Layers grow with every deploy that pulls a new image. A large reclaimable share is old images nothing uses any more; a small one means the space is in images that are still running.
Container writable layers
dockerUsage.containersBytes — bytes containers have written to their own writable layer, on top of the image.
This should stay small. A container writing gigabytes into its writable layer is logging or caching to the wrong place — data that belongs in a volume, and that disappears when the container is recreated.
Volumes
| Series | Wire name | What it is |
|---|---|---|
| Volumes | dockerUsage.volumesBytes | Bytes in named and anonymous volumes |
| Reclaimable (unreferenced) | dockerUsage.volumesReclaimableBytes | Bytes in volumes no container references |
Volumes are where databases and uploads live, so used growing is usually the application growing. Reclaimable volumes are leftovers from removed containers — safe to prune only if nothing needs that data back.
Build cache
| Series | Wire name | What it is |
|---|---|---|
| Build cache | dockerUsage.buildCacheBytes | Bytes held by the builder's cache |
| Reclaimable (not in use) | dockerUsage.buildCacheReclaimableBytes | Cache entries no recent build touched |
A host that builds images on deploy accumulates cache quickly. Almost all of it is reclaimable at the cost of slower next builds.
Object counts
| Series | Wire name | What it is |
|---|---|---|
| Images | dockerUsage.imagesCount | Images on disk |
| Containers | dockerUsage.containersCount | Containers, running or stopped |
| Volumes | dockerUsage.volumesCount | Volumes |
Counts rising while bytes stay flat is many small objects — usually stopped containers or dangling images from repeated deploys. Every reclaimable series above is what a prune would free — dangling images, unreferenced volumes, unused cache — never a projection of deleting live objects.
Related
- Storage usage — the Docker total alongside hosting, backup, and logs
- Storage — how the disk underneath is behaving
- License tiers — why S1 shows a notice here
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