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From "Eli Collins (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2733) Document HA configuration and CLI
Date Mon, 06 Feb 2012 09:07:59 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2733?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13201160#comment-13201160
] 

Eli Collins commented on HDFS-2733:
-----------------------------------

Looks good. Comments follow.

* Might make sense to use machine and host consistently (maybe pick one).
* In the "option of running two redundant NameNodes" paragraph would mention that we now "support
an Active/Passive configuration with a hot standby" since that's the standard HA description
for our configuration.
* Perhaps be explicit that there are two types of state, persistent and ephemeral state. That
all persistent state modifications and some emphemeral (eg block allocation) are logged, with
the remaining ephemeral state (block reports) are handled by the Datanodes communicating two
both Namenodes.
* Might be worth mentioning that we fence both with the fencers but the NNs also fence operations
outside the edits log (eg operations from block reports)
* In the NFS server section, technically there's no requirement it be an NFS server. Would
mention that the availability of the system is limited by the availability of the shared edits
dir, therefore in order to remove all single points of failure there needs to be redundancy
for the shared edits dir. Specifically, multiple network paths to the storage, and redundancy
in the storage itself (disk, network and power).
* Perhaps mention that today manual failover is supported and automatic failover is coming?
* Can mention explicitly that the NN/SBN layout allows people to re-use their existing 2NN/SBN
hardware configuration.
* s/any change/change/
* Wrt syncing metadata directories, perhaps worth noting that you only need to sync the edits
directory since the shared edits dir only contains edits (people may be confused why the old
image they copied there never gets updated)
* Should mention that checkHealth currently doesn't do anything
                
> Document HA configuration and CLI
> ---------------------------------
>
>                 Key: HDFS-2733
>                 URL: https://issues.apache.org/jira/browse/HDFS-2733
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: documentation, ha
>    Affects Versions: HA branch (HDFS-1623)
>            Reporter: Eli Collins
>            Assignee: Aaron T. Myers
>         Attachments: HDFS-2733-HDFS-1623.patch, HDFS-2733-HDFS-1623.patch, HDFSHighAvailability.html,
HDFSHighAvailability.html
>
>
> We need to document the configuration changes in HDFS-2231 and the new CLI introduced
by HADOOP-7774.

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