[ 
http://issues.apache.org/jira/browse/HADOOP-56?page=comments#action_12367623 ] 

eric baldeschwieler commented on HADOOP-56:
-------------------------------------------

As I understand the failure, we brought up a new nameserver on an old cluster 
(so no file information).  The nameserver saw all the blocks of the old FS and 
decided they must all belong to deleted files.  It then proceeded to remove 
them!!

This is bad.  We should have enough interlocks in place that in this situation 
the name server haults and asks for help.  This is not only a risk during 
upgrades!  Other operator failures could cause huge data lose.

> hadoop nameserver does not recognise ndfs nameserver image
> ----------------------------------------------------------
>
>          Key: HADOOP-56
>          URL: http://issues.apache.org/jira/browse/HADOOP-56
>      Project: Hadoop
>         Type: Bug
>   Components: dfs
>     Versions: 0.1
>     Reporter: Yoram Arnon
>     Priority: Critical
>  Attachments: ndfs.tar.gz
>
> hadoop nameserver does not recognise ndfs image
> Thus, upgrading from ndfs to hadoop dfs results in total data loss.
> The upgrade should be seemless, with the new server recognising all previous 
> version that are not end-of-life'd.

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