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https://issues.apache.org/jira/browse/HDFS-2006?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13980468#comment-13980468
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Andrew Purtell commented on HDFS-2006:
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bq. Do you know if there is a common upper bound implemented by other file
systems, like the ext family?
FWIW, from http://en.wikipedia.org/wiki/Extended_file_attributes
{quote}
For ext2/3/4 and btrfs, each extended attribute is limited to a filesystem
block (e.g. 4 KiB), and in practice in ext2/3/4 all of them must fit together
on a single block (including names and values). ReiserFS allow attributes of
arbitrary size. In XFS the names can be up to 256 bytes in length, terminated
by the first 0 byte, and the values can be up to 64KB of arbitrary binary data.
{quote}
In EXT4, all xattrs for a dentry must fit in the inode plus one additional
block. In XFS small attr lists are packed into the inode, large attr lists are
structured externally as a btree, with IIRC no upper limit on number. Its a
large difference in design philosophy.
> ability to support storing extended attributes per file
> -------------------------------------------------------
>
> Key: HDFS-2006
> URL: https://issues.apache.org/jira/browse/HDFS-2006
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Affects Versions: HDFS XAttrs (HDFS-2006)
> Reporter: dhruba borthakur
> Assignee: Yi Liu
> Attachments: HDFS-XAttrs-Design-1.pdf, HDFS-XAttrs-Design-2.pdf,
> xattrs.1.patch, xattrs.patch
>
>
> It would be nice if HDFS provides a feature to store extended attributes for
> files, similar to the one described here:
> http://en.wikipedia.org/wiki/Extended_file_attributes.
> The challenge is that it has to be done in such a way that a site not using
> this feature does not waste precious memory resources in the namenode.
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