Skill

render-disks

Name: render-disks
Author: OpenAI

manage persistent disks on Render services

Published by OpenAI Updated Jun 30

Covers Render File Storage Deployment Storage

Description

Attaches and manages persistent disks on Render services—mount paths, sizing, snapshots, file transfers, and single-instance constraints. Use when the user needs persistent storage, file uploads, a custom database on disk, CMS media storage, or needs to understand why their service can't scale horizontally or use zero-downtime deploys. Trigger terms: persistent disk, disk, storage, mount path, sizeGB, SSD, file uploads, snapshots, disk restore, ephemeral filesystem.

SKILL.md

Render Persistent Disks

Persistent disks are high-performance SSDs you attach to a Render service to preserve filesystem changes across deploys and restarts. Without a disk, services have an ephemeral filesystem—all local file changes are lost on every deploy.

When to Use

Storing file uploads, CMS media, or user-generated content
Running a self-managed database (MySQL, MongoDB, ClickHouse) on Render
Deploying stateful infrastructure (Elasticsearch, Kafka, RabbitMQ, Mattermost)
Understanding why scaling is blocked or zero-downtime deploys are disabled
Restoring data from an automatic disk snapshot

For managed databases, prefer Render Postgres (render-postgres) or Key Value (render-keyvalue) over self-managed alternatives on disk.

Critical Constraints

These constraints affect architecture decisions. Understand them before attaching a disk:

Constraint	Impact
Single instance only	Cannot scale horizontally (`numInstances` must be 1, autoscaling not available)
No zero-downtime deploys	Old instance stops before new instance starts (brief downtime on each deploy)
Runtime access only	Disk is not available during `buildCommand` or `preDeployCommand` (those run on separate compute)
Not accessible from other services	Only the attached service can read/write the disk
Not available on cron jobs	Attach to a web service, private service, or background worker instead
Not available on one-off jobs	One-off jobs run on separate compute without disk access
Can increase size, cannot decrease	Start small and grow as needed

Setup

Dashboard

Go to your service's Disks page
Set the mount path (absolute path where persistent data is stored)
Choose a size in GB
Click Add disk — triggers a new deploy

Blueprint

services:
  - type: web
    name: cms
    runtime: node
    plan: starter
    region: oregon
    buildCommand: npm ci && npm run build
    startCommand: npm start
    disk:
      name: cms-data
      mountPath: /var/data
      sizeGB: 10

Mount Path

Only files written under the mount path are preserved. Everything else remains ephemeral.

Runtime	Source code path	Example mount path
Node.js, Python, Ruby, Elixir, Rust	`/opt/render/project/src`	`/opt/render/project/src/uploads`
Go	`/opt/render/project/go/src/github.com/<user>/<repo>`	`.../data`
Docker	Dockerfile's `WORKDIR` (commonly `/app`)	`/app/storage`

Disallowed mount paths

Cannot mount at: /, /opt, /opt/render, /opt/render/project, /opt/render/project/src, /home, /home/render, /etc, /etc/secrets.

Subdirectories of these paths are fine (e.g. /opt/render/project/src/uploads).

Snapshots

Render creates an automatic snapshot every 24 hours
Snapshots are available for at least 7 days
Restore from the service's Disks page in the Dashboard
Full restore only — you cannot restore individual files
Destructive — all changes after the snapshot are lost

Do not restore snapshots for custom database recovery. Use database-native backup tools (mysqldump, mongodump) instead—disk snapshots may capture a corrupted database state.

File Transfers

SCP (via SSH)

# Download from service
scp -s YOUR_SERVICE@ssh.YOUR_REGION.render.com:/mount/path/file ./local-file

# Upload to service
scp -s ./local-file YOUR_SERVICE@ssh.YOUR_REGION.render.com:/mount/path/file

Requires SSH access enabled for the service.

Magic-Wormhole

Available on all native runtimes (install manually on Docker):

# On the service shell
wormhole send /mount/path/file

# On your local machine
wormhole receive

Common Patterns

Pattern	Service type	Mount path	Notes
WordPress / Ghost / CMS	Web Service	`/var/data` or `/app/content`	Media uploads, SQLite
Self-managed MySQL	Private Service	`/var/lib/mysql`	Use mysqldump for backups, not disk snapshots
File upload API	Web Service	`/opt/render/project/src/uploads`	Single instance constraint
Elasticsearch	Private Service	`/usr/share/elasticsearch/data`	Stateful search infrastructure

Common Mistakes

Mistake	Fix
Expecting horizontal scaling with a disk	Not possible — disk services are single-instance only
Mounting at a disallowed path	Use a subdirectory (e.g. `/opt/render/project/src/uploads` not `/opt/render/project/src`)
Reading disk during build or pre-deploy	These run on separate compute — move logic to the start command
Restoring disk snapshot for a database	Use database-native backups instead
Starting with a large disk size	Start small — you can increase but never decrease

References

Document	Contents
`references/sizing-and-snapshots.md`	Sizing guidance, snapshot lifecycle, restore procedures, cost patterns

render-web-services — Deploy lifecycle, health checks (disk disables zero-downtime)
render-private-services — Internal services with disks (Elasticsearch, MySQL)
render-blueprints — disk field reference in render.yaml
render-postgres — Managed database alternative (no disk management needed)

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