Daryn Sharp created HDFS-8486:
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Summary: DN startup may cause severe data loss
Key: HDFS-8486
URL: https://issues.apache.org/jira/browse/HDFS-8486
Project: Hadoop HDFS
Issue Type: Bug
Components: datanode
Affects Versions: 2.0.0-alpha, 0.23.1
Reporter: Daryn Sharp
Assignee: Daryn Sharp
Priority: Blocker
A race condition between block pool initialization and the directory scanner
may cause a mass deletion of blocks in multiple storages.
If block pool initialization finds a block on disk that is already in the
replica map, it deletes one of the blocks based on size, GS, etc.
Unfortunately it _always_ deletes one of the blocks even if identical, thus the
replica map _must_ be empty when the pool is initialized.
The directory scanner starts at a random time within its periodic interval
(default 6h). If the scanner starts very early it races to populate the
replica map, causing the block pool init to erroneously delete blocks.
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