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Date: Tue, 1 Sep 2009 09:24:33 -0700 (PDT)
From: "Sanjay Radia (JIRA)" <jira@apache.org>
To: hdfs-issues@hadoop.apache.org
Subject: [jira] Commented: (HDFS-578) Support for using server default
 values for blockSize and replication when creating a file
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    [ https://issues.apache.org/jira/browse/HDFS-578?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12749968#action_12749968 ] 

Sanjay Radia commented on HDFS-578:
-----------------------------------

This is closely tied to HADOOP-4952 (so please refer to that) which states that we support options 1 and 2 but not 3:
# Specify the desired values as explict parameters in the methods such as create. [as in current system]
# Use SS defaults - different FS and their deployments can have their own defaults and also frees the admin from distributing the default config to all client nodes. [New]
# Use client side defaults derived from the config. [ is in current system]

It also proposes that there are no per FileSystem defaults, only per deployment SS defaults (see HADOOP-4952 for details).

What it means is that one does not need fs config variables except for the default fs in the config.
This works well for everything except the bytesPerChecksum, because the create call does not have parameter called bytesPerChecksum.
If application configurable bytesPerChecksum is important then there are two options: (a) add it as a parameter to the create call (most folks
will get confused by what to set) or (b) support options 3. If we support option 3 then to be consistent we should probably support it for all parameters (blkSize, repFac, buffer size, etc). 

> Support for using server default values for blockSize and replication when creating a file
> ------------------------------------------------------------------------------------------
>
>                 Key: HDFS-578
>                 URL: https://issues.apache.org/jira/browse/HDFS-578
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: hdfs client, name-node
>            Reporter: Kan Zhang
>            Assignee: Kan Zhang
>
> This is a sub-task of HADOOP-4952. This improvement makes it possible for a client to specify that it wants to use the server default values for blockSize and replication params when creating a file.

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