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Disks

Miren Disks provide persistent storage for your applications. Unlike ephemeral container storage that disappears when your app restarts, disks preserve your data across deployments, restarts, and even cluster migrations.

Why Use Disks?​

  • Persistent data: Store databases, uploads, cache files, or any data that needs to survive restarts
  • Portable across clusters: Your disk data is automatically synced to Miren Cloud and can be restored on any cluster
  • Automatic backups: Data is replicated to Miren Cloud, giving you peace of mind
  • Simple configuration: Just specify a disk name and mount path in your app config

How Disks Work​

When you configure a disk for your application:

  1. Miren creates the disk with the size and filesystem you specify
  2. Your app instance acquires a lease on the disk (exclusive access)
  3. The disk is mounted at the path you specified in your container
  4. Data is replicated to Miren Cloud in the background

When your app stops or restarts:

  • The lease is released
  • Data remains on the disk
  • Your next instance can acquire the lease and continue where it left off

How Much Storage Does Miren Provide?​

During the Developer Preview, we're providing unmetered storage. The intention is to implement a free tier and usage based pricing on the storage. We'll be sure to communicate often and clearly how we intend to proceed.

The feature is designed to keep our costs low, and our intention is to pass that low cost on to our users.

Configuring Disks​

Add a disk to your application by including a disks section in your service configuration in .miren/app.toml:

[services.web]
image = "myapp:latest"

[[services.web.disks]]
name = "my-app-data"
mount_path = "/data"
size_gb = 10
filesystem = "ext4"

Configuration Options​

OptionRequiredDescription
nameYesUnique name for the disk (alphanumeric, hyphens allowed)
mount_pathYesWhere to mount the disk in your container
size_gbYes*Size in gigabytes (required for auto-creation)
filesystemNoFilesystem type: ext4 (default), xfs, or btrfs
read_onlyNoMount as read-only (default: false)

*size_gb is required when the disk doesn't already exist. If the disk exists, this field is ignored.

Example: PostgreSQL with Persistent Storage​

[services.db]
image = "postgres:16"

[[services.db.env]]
key = "POSTGRES_PASSWORD"
value = "secret"

[[services.db.env]]
key = "PGDATA"
value = "/var/lib/postgresql/data/pgdata"

[[services.db.disks]]
name = "myapp-postgres"
mount_path = "/var/lib/postgresql/data"
size_gb = 20
filesystem = "ext4"

Example: File Upload Storage​

[services.web]
image = "myapp:latest"

[[services.web.disks]]
name = "myapp-uploads"
mount_path = "/app/uploads"
size_gb = 50

Disk Lifecycle​

Creation​

Disks are automatically created when your app first deploys with a volume configuration that includes size_gb. The disk is provisioned with the specified size and filesystem.

Reuse​

If you deploy an app with a disk_name that already exists, Miren will attach the existing disk instead of creating a new one. This allows you to:

  • Share data between app versions
  • Preserve data across complete redeployments
  • Reference disks created by other apps

Deletion​

Disks are not automatically deleted when you delete an app. This is intentional - your data is precious. To delete a disk:

miren debug disk delete -i <disk-id>

Viewing Disks in Miren Cloud​

When connected to Miren Cloud, you can view and monitor your disks:

  1. Dashboard: See all disks across your clusters with their status and usage
  2. Data sync status: Monitor replication progress to the cloud
  3. Disk history: View when disks were created, attached, and modified

Visit miren.cloud and navigate to your cluster to view disk details.

Inspecting Disks via CLI​

List all disks:

miren debug disk list

Check a specific disk's status:

miren debug disk status -i <disk-id>

View active disk leases:

miren debug disk lease-list

See CLI Reference - Disk Commands for complete command documentation.

Important Considerations​

One Instance per Disk​

Disks use exclusive leasing - only one app instance can mount a disk at a time. This ensures data consistency but means:

  • Multiple replicas of your app cannot share the same disk
  • If you need shared storage, use separate disks per instance or external storage

Disk Sizing​

  • Disks use a "thin provisioning" technology, enabling it to only allocated storage when needed
  • Choose a size that accommodates growth

Filesystem Choice​

  • ext4: Best general-purpose choice, widely compatible
  • xfs: Better for large files and high-throughput workloads

NOTE: Your server must have the mkfs tools to format the disk types.

Next Steps​