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https://issues.apache.org/jira/browse/HADOOP-1242?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12496371
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Konstantin Shvachko commented on HADOOP-1242:
---------------------------------------------
I think we should target a more general task here (if any), which could be
called "backward incompatibility" I guess.
Namely, a conversion from a pre-upgrade layout versions to the current one
should be performed in a way that
any attempt to run old version hdfs software in converted repository would fail.
- For data-nodes this can be achieved by retaining the storage file in its
original location but updating its
version to a newer one. That way the old data-node code will complain about not
being able to read
future version storage.
- For the name-node we can also write the new version into the old image file
or corrupt the image in any other way,
say by placing a message inside "This image is corrupted intentionally. Please
do not remove."
The only drawback of this approach I can see is that the old storage and image
files will have to stay
in the repositories forever, and even if you create a hdfs from scratch old
files will still need to be created
if we want to support backward incompatibility.
> dfs upgrade/downgrade problems
> ------------------------------
>
> Key: HADOOP-1242
> URL: https://issues.apache.org/jira/browse/HADOOP-1242
> Project: Hadoop
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.13.0
> Reporter: Owen O'Malley
> Assigned To: Konstantin Shvachko
> Priority: Blocker
> Fix For: 0.13.0
>
> Attachments: clean-upgrade.patch
>
>
> I ran my test cluster on 0.13 and then tried to run it under 0.12. When I
> downgraded, the namenode would not come up and the message said I needed to
> format the filesystem. I ignored that and tried to restart on 0.13, now the
> datanode will not come up with:
> 2007-04-10 11:25:37,448 ERROR org.apache.hadoop.dfs.DataNode:
> org.apache.hadoop.
> dfs.InconsistentFSStateException: Directory /local/owen/hadoop/dfs/d
> ata is in an inconsistent state: Old layout block directory
> /local/owen/hadoop/dfs/data/data is missing
> at
> org.apache.hadoop.dfs.DataStorage.isConversionNeeded(DataStorage.java
> :170)
> at
> org.apache.hadoop.dfs.Storage$StorageDirectory.analyzeStorage(Storage
> .java:264)
> at
> org.apache.hadoop.dfs.DataStorage.recoverTransitionRead(DataStorage.j
> ava:83)
> at org.apache.hadoop.dfs.DataNode.startDataNode(DataNode.java:230)
> at org.apache.hadoop.dfs.DataNode.<init>(DataNode.java:199)
> at org.apache.hadoop.dfs.DataNode.makeInstance(DataNode.java:1175)
> at org.apache.hadoop.dfs.DataNode.run(DataNode.java:1119)
> at org.apache.hadoop.dfs.DataNode.createDataNode(DataNode.java:1140)
> at org.apache.hadoop.dfs.DataNode.main(DataNode.java:1299)
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