[
https://issues.apache.org/jira/browse/HADOOP-1134?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]
Raghu Angadi updated HADOOP-1134:
---------------------------------
Attachment: bc-no-upgrade-05302007.patch
Current patch is attached. This is a VERY EXPERIMENTAL patch. A few notes:
# Applies to trunk as of 05/30/07.
# This will not start on existing DFS. You need first format with this patch.
# DFS is fully functional and is not expected be any slower than current DFS.
But this in no way close to being final patch.
# There is a bug chunk of Upgrade related in DataNode.java and a little bit in
FSNameSystem.java but it is not currently excuted.
# {{DistributedFileSystem}} in trunk becomes {{ChecsumDistributedFileSystem}}
with the patch. {{DistributeFileSystem}} in the patch does not create {{.crc}}
files.
# Core functionality and protocol is described in the html file attached with
previous comment.
# The important changes are in DFSClient.java and DataNode.java
# DFSClient.BlockReader class handles reading from a datanode and unpacks the
data.
# There are quite a few {{XXX}} comments and will be handled in later patches.
> Block level CRCs in HDFS
> ------------------------
>
> Key: HADOOP-1134
> URL: https://issues.apache.org/jira/browse/HADOOP-1134
> Project: Hadoop
> Issue Type: New Feature
> Components: dfs
> Reporter: Raghu Angadi
> Assignee: Raghu Angadi
> Attachments: bc-no-upgrade-05302007.patch,
> DfsBlockCrcDesign-05305007.htm
>
>
> Currently CRCs are handled at FileSystem level and are transparent to core
> HDFS. See recent improvement HADOOP-928 ( that can add checksums to a given
> filesystem ) regd more about it. Though this served us well there a few
> disadvantages :
> 1) This doubles namespace in HDFS ( or other filesystem implementations ). In
> many cases, it nearly doubles the number of blocks. Taking namenode out of
> CRCs would nearly double namespace performance both in terms of CPU and
> memory.
> 2) Since CRCs are transparent to HDFS, it can not actively detect corrupted
> blocks. With block level CRCs, Datanode can periodically verify the checksums
> and report corruptions to namnode such that name replicas can be created.
> We propose to have CRCs maintained for all HDFS data in much the same way as
> in GFS. I will update the jira with detailed requirements and design. This
> will include same guarantees provided by current implementation and will
> include a upgrade of current data.
>
--
This message is automatically generated by JIRA.
-
You can reply to this email to add a comment to the issue online.
