[HDFS-903] NN should verify images and edit logs on startup

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Fix Version/s: 0.22.0
• Component/s: namenode
• Hadoop Flags: Incompatible change, Reviewed
• Release Note: Store fsimage MD5 checksum in VERSION file. Validate checksum when loading a fsimage. Layout version bumped.
• Assignee: Hairong Kuang
• Reporter: Eli Collins
• Created: 15/Jan/10 23:27
• Updated: 19/Jul/14 00:02
• Resolved: 08/Nov/10 06:52

Description

I was playing around with corrupting fsimage and edits logs when there are multiple dfs.name.dirs specified. I noticed that:

• As long as your corruption does not make the image invalid, eg changes an opcode so it's an invalid opcode HDFS doesn't notice and happily uses a corrupt image or applies the corrupt edit.
• If the first image in dfs.name.dir is "valid" it replaces the other copies in the other name.dirs, even if they are different, with this first image, ie if the first image is actually invalid/old/corrupt metadata than you've lost your valid metadata, which can result in data loss if the namenode garbage collects blocks that it thinks are no longer used.

How about we maintain a checksum as part of the image and edit log and check those on startup and refuse to startup if they are different. Or at least provide a configuration option to do so if people are worried about the overhead of maintaining checksums of these files. Even if we assume dfs.name.dir is reliable storage this guards against operator errors.

Issue Links

• blocks: HDFS-1481 NameNode should validate fsimage before rolling
• breaks: HDFS-1500 TestOfflineImageViewer failing on trunk
• contains: HDFS-52 SecondaryNameNode should validate the downloaded files.
• is blocked by: HADOOP-7009 MD5Hash provides a public factory method that creates an instance of MessageDigest
• is related to: HDFS-1496 TestStorageRestore is failing after HDFS-903 fix
• relates to: HDFS-1382 A transient failure with edits log and a corrupted fstime together could lead to a data loss
• relates to: HDFS-1602 NameNode storage failed replica restoration is broken
• relates to: HDFS-1458 Improve checkpoint performance by avoiding unnecessary image downloads