Andrew Wang commented on HDFS-11009:

Thanks for working on this Xiao. Looks good overall, though a few review 

* Looks like both the block and out files are required parameters, so no please 
do not use "[]" in the help text and doc. It's also debatable whether these 
should be flags at all, since UNIX normally uses positional args if they're 
* I'm mixed on this one, but it'd be more clear if this command was named 
"computeMeta". Unfortunately there's also the existing "verify" command, and 
the commands are named "*BlockChecksumCommand". The debug command comes with no 
compat guarantees, so maybe we do some renames even for branch-2.
* It'd also be nice to add some disclaimers to the doc/help text. I'm guessing 
this is meant for use in emergency situations where the block only has corrupt 
replicas? I'm also wondering about the danger of divergent state on different 
DNs, since I don't think HDFS-level mechanisms like the BlockScanner or FBRs 
will catch this.

> Add a tool to reconstruct block meta file from CLI
> --------------------------------------------------
>                 Key: HDFS-11009
>                 URL: https://issues.apache.org/jira/browse/HDFS-11009
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: datanode
>            Reporter: Xiao Chen
>            Assignee: Xiao Chen
>         Attachments: HDFS-11009.01.patch, HDFS-11009.02.patch
> If the block file on local disk presents, but the meta file is missing, it's 
> theoretically possible to manually restore the meta file and have the block 
> readable.
> This jira is to propose to add such a tool to do that.

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