longhorn/enhancements/20230309-recurring-filesystem-trim.md

Recurring Filesystem Trim

Summary

Longhorn currently supports the filesystem trim feature, which allows users to reclaim volume disk spaces of deleted files. However, this is a manual process, which can be time-consuming and inconvenient.

To improve user experience, Longhorn could automate the process by implementing a new RecurringJob filesystem-trim type. This enhancement enables regularly freeing up unused volume spaces and reducing the need for manual interventions.

Related Issues

https://github.com/longhorn/longhorn/issues/5186

Motivation

Goals

Introduce a new recurring job type called filesystem-trim to periodically trim the volume filesystem to reclaim disk spaces.

Non-goals [optional]

None

Proposal

To extend the RecurringJob custom resource definition by adding new RecurringJobType: filesystem-trim.

User Stories

To schedule regular volume filesystem trims, user can create a RecurringJob with spec.task=filesystem-trim and associating it with volumes.

User Experience In Detail

Recurring Filesystem Trim

1. The user sees workload volume size has increased over time.
2. Create RecurringJob with the filesystem-trim task type and assign it to the volume.

   apiVersion: longhorn.io/v1beta2
   kind: RecurringJob
   metadata:
     name: recurring-fs-trim-per-min
     namespace: longhorn-system
   spec:
     concurrency: 1
     cron: '* * * * *'
     groups: []
     labels: {}
     name: recurring-fs-trim-per-min
     retain: 0
     task: filesystem-trim
   

3. The RecurringJob runs and relaims some volume spaces.

API changes

None

Design

Implementation Overview

The RecurringJob filesystem-trim Task Type

1. Call Volume API ActionTrimFilesystem when the RecurringJob type is filesystem-trim.

RecurringJob Mutate

1. Mutate the Recurringjob.Spec.Retain to 0 when the task type is filesystem-trim as it is not effective for this type of task.

Test plan

Test Recurring Filesystem Trim

1. Create workload.
2. Create a file with some data in the workload.
3. Volume actual size should increase.
4. Delete the file.
5. Volume actual size should not decrease.
6. Create RecurringJob with type filesystem-trim and assign to the workload volume.
7. Wait for RecurringJob to complete.
8. Volume actual size should decrease.

Upgrade strategy

None

Note [optional]

None