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https://issues.apache.org/jira/browse/HDFS-8681?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14603991#comment-14603991
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Chris Nauroth commented on HDFS-8681:
-------------------------------------
The old logic, pre-HDFS-7430, was as Arpit described, disabling only for a
negative value.
{code}
private synchronized void initDataBlockScanner(Configuration conf) {
if (blockScanner != null) {
return;
}
String reason = null;
assert data != null;
if (conf.getInt(DFS_DATANODE_SCAN_PERIOD_HOURS_KEY,
DFS_DATANODE_SCAN_PERIOD_HOURS_DEFAULT) < 0) {
reason = "verification is turned off by configuration";
} else if ("SimulatedFSDataset".equals(data.getClass().getSimpleName())) {
reason = "verifcation is not supported by SimulatedFSDataset";
}
if (reason == null) {
blockScanner = new DataBlockScanner(this, data, conf);
blockScanner.start();
} else {
LOG.info("Periodic Block Verification scan disabled because " + reason);
}
}
{code}
Backwards-compatibility requires that we restore that logic. Otherwise, if
someone had a hdfs-site.xml file that set {{dfs.datanode.scan.period.hours}} to
0 explicitly, then it would stop working.
> BlockScanner is incorrectly disabled by default
> -----------------------------------------------
>
> Key: HDFS-8681
> URL: https://issues.apache.org/jira/browse/HDFS-8681
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 2.7.0
> Reporter: Andrew Wang
> Assignee: Colin Patrick McCabe
> Priority: Blocker
>
> This code is used to check whether the block scanner is enabled:
> {noformat}
> public boolean isEnabled() {
> return (conf.scanPeriodMs) > 0 && (conf.targetBytesPerSec > 0);
> }
> {noformat}
> Unfortunately, when this was introduced, we did not change the default scan
> period's value of 0, which means by default the BlockScanner is disabled.
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