Longhorn: [Question] Minimal volume size

[Angelinsky7]

Hi,
i would like to know if it's possible (and how) to create volumes smaller that 1Gi in size.
when i try to build a smaller volume in rancher, longhorn always create 1Gi volume....

if you look at this kubernetes volume file you can see that i tried to create a 400Mi volume but longhorn created a 1Gi one.

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  annotations:
    control-plane.alpha.kubernetes.io/leader: '{"holderIdentity":"297fad77-060f-11e9-8d7b-8ea00bc77d09","leaseDurationSeconds":15,"acquireTime":"2019-01-05T14:50:25Z","renewTime":"2019-01-05T14:50:27Z","leaderTransitions":0}'
    pv.kubernetes.io/bind-completed: "yes"
    pv.kubernetes.io/bound-by-controller: "yes"
    volume.beta.kubernetes.io/storage-provisioner: rancher.io/longhorn
  creationTimestamp: 2019-01-05T14:50:25Z
  finalizers:
  - kubernetes.io/pvc-protection
  labels:
    app: nextcloud-apps
    chart: nextcloud-1.0.0-apps
    heritage: Tiller
    instance: nextcloud-wggng
    io.cattle.field/appId: nextcloud-wggng
  name: nextcloud-wggng-apps
  namespace: nextcloud-wggng
  resourceVersion: "1895891"
  selfLink: /api/v1/namespaces/nextcloud-wggng/persistentvolumeclaims/nextcloud-wggng-apps
  uid: 3c0cf148-10f9-11e9-8f38-e0d55e2e2e44
spec:
  accessModes:
  - ReadWriteOnce
  resources:
    requests:
      storage: 400Mi
  storageClassName: longhorn
  volumeName: pvc-3c0cf14810f911e9
status:
  accessModes:
  - ReadWriteOnce
  capacity:
    storage: 1Gi
  phase: Bound

is this normal ? thanks a lot for your answers

[yasker]

@Angelinsky7 I think in the manager we've limited the minimal size of the volume to 1G. I need to check but I agree that we should able to create volume less than 1G. 1 MiB sounds like a reasonable minimum.

[yasker]

On second thought, 1G sounds fine too. Since Longhorn is sparse, so unused storage won't take space anyway.

[Angelinsky7]

Thanks for you answer, i would gladly prefer a 1Mi minimum limit like that i could create 1Mi maximum storage. If you see what i mean... (or a 500Mi maximum redis cache, or db or anything that i would like)
with the 1Gi minimum limit it also mean that every storage can be 1Gi and in some case i would prefer not (like that i can be completely sure of my storage usage)

[yasker]

1MiB minimal sounds a bit too small. I think 10MiB can be used as the minimal.

[dbaker-rh]

Thank you for the update, yasker. Let me know if I can help test anything en route to 1.1.0.

(definitely agree. 1MIB is way too small. 10MiB is still a little on the small side, so wouldn't be unhappy if it turned into 50MiB)

[longhorn-io-github-bot]

Pre-merged Checklist

• [x] Does the PR include the explanation for the fix or the feature?

• [x] Is the backend code merged (Manager, Engine, Instance Manager, BackupStore etc)?
  The PR is at https://github.com/longhorn/longhorn-manager/pull/730

• [x] Is the reproduce steps/test steps documented?

• [x] ~~Which areas/issues this PR might have potential impacts on?
  Area CSI Provisioning.
  Issues

• [x] If the fix introduces the code for backward compatibility Has an separate issue been filed with the label release/obsolete-compatibility?
  The compatibility issue is filed at

• [x] If labeled: area/ui Has the UI issue filed or ready to be merged?
  The UI issue/PR is at

• [x] if labeled: require/doc Has the necessary document PR submitted or merged?
  The Doc issue/PR is at

• [x] If labeled: require/automation-e2e Has the end-to-end test plan been merged? Have QAs agreed on the automation test case?
  The automation skeleton PR is at https://github.com/longhorn/longhorn-tests/pull/447
  The automation test case PR is at

• [x] if labeled: require/automation-engine Has the engine integration test been merged?
  The engine automation PR is at

• [x] if labeled: require/manual-test-plan Has the manual test plan been documented?
  The updated manual test plan is at

[khushboo-rancher]

Verified with longhorn-master - 10/28/2020

Validation - Pass

1. Created below PVC with 5 Mi, the longhorn volume and PVC got created with 10 Mi.

apiVersion: v1
kind: PersistentVolumeClaim
metadata:
  name: longhorn-simple-5
  namespace: default
spec:
  accessModes:
    - ReadWriteOnce
  storageClassName: longhorn
  resources:
    requests:
      storage: 5Mi

1. Created PVC with 10Mi, longhorn volume and PVC got created with 10Mi storage.
2. Created PVC with 1Gi, longhorn volume and PVC got created with 1Gi storage.
3. Created PVC with 2Gi, longhorn volume and PVC got created with 2Gi storage.

Validated the read/write snapshot and backup functionality of above created volume.

log on creating PVC smaller than 10Mi, the request has 10Mi size.

[longhorn-manager-l5qhq] 10.42.1.63 - - [28/Oct/2020:19:42:59 +0000] "GET /v1/volumes/pvc-6b289b20-371d-4ce0-9d21-2949581df1ce HTTP/1.1" 404 0 "" "Go-http-client/1.1" 
[longhorn-manager-l5qhq] time="2020-10-28T19:42:59Z" level=debug msg="Created volume pvc-6b289b20-371d-4ce0-9d21-2949581df1ce: {Size:10485760 Frontend:blockdev FromBackup: NumberOfReplicas:3 DataLocality:disabled StaleReplicaTimeout:2880 NodeID: EngineImage:longhornio/longhorn-engine:master RecurringJobs:[] BaseImage: Standby:false DiskSelector:[] NodeSelector:[] DisableFrontend:false RevisionCounterDisabled:false}" 

[khushboo-rancher]

The integration test test_csi_minimal_volume_size has been passing in the nightly run since merged.