[HDDS-9125] Decommissioning blocked because of under replicated EC containers

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.4.0
• Fix Version/s: 1.4.0
• Component/s: ECOfflineRecovery, SCM
• Target Version/s: 1.4.0
• Assignee: Stephen O'Donnell
• Reporter: Siddhant Sangwan
• Created: 07/Aug/23 06:01
• Updated: 22/Jan/24 12:58
• Resolved: 07/Sep/23 11:28

Description

The situation is well documented under the heading 'Situation 4' in https://docs.google.com/document/d/1ebuSwJZkw4wMWWCHinDvRCfNbeFD4kcHMyIN6Q6wD9g/edit?usp=sharing. This happens because of limitations in rack scatter policy + replication manager flow. One possible solution is implementing "fallback" in the rack scatter policy. Along with the doc, this PR is also related - https://github.com/apache/ozone/pull/5097.

An example (summary) of this situation:
Suppose there are 5 racks and 6 DNs, such that any one rack will have 2 DNs. 5 replicas of an EC container are scattered across each of the 5 racks (so that there's only 1 replica on each rack). Now, if any of the Datanodes from any rack where there's only 1 DN on that rack is decommissioned, under replication handling will be blocked.

Issue Links

• links to: PR 5246