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https://issues.apache.org/jira/browse/HBASE-17437?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15815934#comment-15815934
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Sean Busbey commented on HBASE-17437:
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My read of the patch had the wal root dir default to the same as the hbase root
door, and that's fine by me; I have no desire to default the wal dir being
outside of the hbase root dir. but if it's set I'd prefer we save future heart
ache by ensuring we aren't setting ourselves up for writing within the hbase
root dir in a way different from when this config isn't used. Otherwise we run
the risk of incorrect assumptions about what is written into various
directories within the hbase root dir. I would not want to rely on things being
correct, for example, if the wal root dir was set to the archive or oldWALs
location. I don't know what future assumptions we'll make about the hbase root
dir, so better to just say "if you want to set this somewhere else, it has to
be somewhere entirely different than our root dir."
I don't have strong feelings on config naming; anything that accurately
reflects the use is fine. For example, {{hbase.wal.dir}} and
{{hbase.wal.dir.perms}} would be accurate. A note that the config is used both
for RegionServer WALs and Master Procedure WALs would help avoid future
questions about why the permission isn't named as a regionserver-specific
property. Also, we should specify WALs are what's stored rather than logs,
since "logs" has a multiple meanings and in the context of HBase deploys
usually refers to a human-consumable record of service activity, e.g. as would
be written to {{/var/log/}}.
> Support specifying a WAL directory outside of the root directory
> ----------------------------------------------------------------
>
> Key: HBASE-17437
> URL: https://issues.apache.org/jira/browse/HBASE-17437
> Project: HBase
> Issue Type: Improvement
> Components: Filesystem Integration, wal
> Affects Versions: 1.2.4
> Reporter: Yishan Yang
> Assignee: Yishan Yang
> Labels: patch
> Fix For: 2.0.0, 1.4.0
>
> Attachments: hbase-17437-branch-1.2.patch, hbase-17437-master.patch
>
>
> Currently, the WAL and the StoreFiles need to be on the same FileSystem. Some
> FileSystems (such as Amazon S3) don’t support append or consistent writes.
> These two properties are imperative for the WAL in order to avoid loss of
> writes. However, StoreFiles don’t necessarily need the same consistency
> guarantees (since writes are cached locally and if writes fail, they can
> always be replayed from the WAL).
>
> This JIRA aims to allow users to configure a log directory (for WALs) that is
> outside of the root directory or even in a different FileSystem. The default
> value will still put the log directory under the root directory.
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