OCI block volumes and custom images to STACKIT

A block volume and a custom image, assessed

A demo estate written for this page and assessed on 4 November 2026 holds two volumes, a custom image, a backup policy and one server. Shown here: the 500 GB data volume. Values are copied from the run. assessment.json is written as a single line, so the pane shows selected fields of each unit, indented and nested as in the file, with the values unchanged.

resource "oci_core_volume" "data" {
  compartment_id      = var.compartment_id
  availability_domain = var.availability_domain
  display_name        = "app-data"
  size_in_gbs         = 500
  vpus_per_gb         = 10
}

{
  "id": "oci_core_volume.data",
  "wave": 1,
  "result": {
    "class": "RECONFIGURE",
    "confidence": "LOW",
    "target": {
      "service": "STACKIT Block Storage"
    },
    "reason": "A block volume becomes a STACKIT volume. The performance setting does not carry over; choose a STACKIT performance class, and move the data at the host or from a backup."
  }
}

• The performance setting does not carry over

  vpus_per_gb has no STACKIT equivalent. The run says so and leaves you to choose a STACKIT performance class.

• Five settings are yours

  availability_domain, compartment_id, display_name, size_in_gbs and vpus_per_gb are listed as critical settings left to you. No STACKIT volume block is written; you set size and class yourself.

The image the run cannot map

The oci_core_image resource is not in the catalogue of this build. It is classified MANUAL_REVIEW, nothing of it is assessed or drafted, and the server that uses it is linked to it with a warning. assessment.json is written as a single line, so the pane shows selected fields of each unit, indented and nested as in the file, with the values unchanged.

resource "oci_core_image" "golden" {
  compartment_id = var.compartment_id
  display_name   = "golden-app-image"
  launch_mode    = "PARAVIRTUALIZED"

  image_source_details {
    source_type    = "objectStorageTuple"
    namespace_name = "examplens"
    bucket_name    = "image-import"
    object_name    = "golden-app.qcow2"
    source_image_type = "QCOW2"
  }
}

{
  "id": "oci_core_image.golden",
  "wave": 1,
  "result": {
    "class": "MANUAL_REVIEW",
    "confidence": "LOW",
    "reason": "oci_core_image is not in the knowledge base catalogue; an architect has to decide the target. Nothing of this resource is assessed or drafted (unknown source type)."
  }
}

The move in order

The wave order comes from the run: image, volumes and backup policy first, then the server and the policy assignment, then the volume attachments.

1. 01

   1. Inventory what is attached

   List every volume, its size, its performance setting, its backup policy and the instance it is attached to. The demo has a 500 GB volume at 10 VPUs per GB and a 100 GB volume at 0, attached to one server by two paravirtualized attachments.

2. 02

   2. Export the image, or find its source

   Oracle can export a custom image to an Object Storage bucket as VMDK, VHD, VDI or QCOW2, or as an .oci file meant for other tenancies and regions. You need write access to the bucket, and the image is in the state Exporting until the file exists. If the file you originally imported is still in your hands, that file is the simpler starting point.

3. 03

   3. Convert and upload to STACKIT

   STACKIT accepts raw, qcow2 and iso images up to 70 GB. For another format, convert with qemu-img convert -O raw. You create the queued image through the IaaS API, receive an image ID and a one-time upload URL that lapses after a few hours, upload the file with an HTTP PUT and check that the state is AVAILABLE.

4. 04

   4. Choose a performance class per volume

   Pick from the STACKIT classes by IOPS and throughput, not by size: the limits of a class do not depend on volume size. Measure the real peak on the source before you choose.

5. 05

   5. Create volumes and move the data

   The run says to move the data at the host or from a backup and records no mechanism: the size of the data, the downtime the business tolerates and the consistency the application needs decide it. The wave order puts the attachments last, so attach the data volumes once the server exists.

6. 06

   6. Recreate backups and verify

   The OCI backup policy and its assignment are MANUAL_REVIEW. STACKIT documents snapshots, full backups and incremental backups for volumes; you define the schedule and retention again.

How the estate mapped

All eight units have LOW confidence. The oci provider is not pinned by a lock file, which caps every unit at MEDIUM; the three catalogued units (both volumes and the server) drop further because they are linked to resources the catalogue does not know, and the five others are not in the catalogue at all. No STACKIT resource block is written for any of the eight.

Performance: where Oracle and STACKIT differ

Oracle scales performance with every gigabyte up to a cap per volume; STACKIT sets it per volume as a class, independent of size. The Oracle ceiling below is computed from Oracle's per-GB rates for the two demo volumes; the STACKIT figures are the EU01 classes on the service-plan page as of November 2026. That page lists no other region, so check the classes again if you land in EU02.

The Oracle figure is a ceiling, not the load: a volume rarely runs at its cap. Measure the real peak IOPS and throughput on the source and choose the smallest class above it; the classes listed are perf0, 1, 2, 4, 6, 8, 10, 12 to 21 and 29.

Decisions the architect owns

• Class per volume

  The 500 GB data volume runs at Balanced, which Oracle caps at 25,000 IOPS for that size; perf14 matches that ceiling. If the measured peak is lower, a smaller class such as perf8 or perf10 may do.

• Availability setup

  STACKIT offers every performance class in a Single AZ and in a Metro AZ setup. Single AZ pins the volume to one zone; Metro AZ mirrors it across two.

• Image route

  Export from Oracle, or rebuild the image from your build pipeline. A rebuild also lets you review what the image contains.

• Data-movement method

  Host-level copy, restore from a backup, or a replication tool: the run records the mechanism as UNKNOWN and the state as DECISION_REQUIRED for both volumes.

• Resize limits

  STACKIT data volumes range from 1 GB to 16 TB; they can be enlarged only while detached and never reduced. OCI volumes range from 50 GB to 32 TB, so a volume above 16 TB has to be split.

Questions infrastructure teams ask

Sources

• Oracle Cloud: Block Volume performance
• Oracle Cloud Terraform provider: core_volume resource
• Oracle Cloud: Exporting custom images
• STACKIT Docs: Use custom images with the IaaS API
• STACKIT Docs: Service plans of Block Storage
• STACKIT Docs: Concepts of Block Storage