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https://issues.apache.org/jira/browse/CASSANDRA-21752?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Nivy Kani updated CASSANDRA-21752:
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Bug Category: Parent values: Correctness(12982)Level 1 values: API /
Semantic Definition(13162)
Complexity: Normal
Discovered By: User Report
Fix Version/s: 7.x
Severity: Normal
Status: Open (was: Triage Needed)
> StartupChecks.checkReadAheadKbSetting does not work with mapped virtual
> devices
> -------------------------------------------------------------------------------
>
> Key: CASSANDRA-21752
> URL: https://issues.apache.org/jira/browse/CASSANDRA-21752
> Project: Apache Cassandra
> Issue Type: Bug
> Components: Feature/Startup Checks
> Reporter: Nivy Kani
> Assignee: Nivy Kani
> Priority: Normal
> Fix For: 7.x
>
>
> The default setting for kernel read ahead is suboptimal for I/O (4096KB), so
> CASSANDRA-16436 previously added a startup check to warn operators when it’s
> misconfigured.
> However, this check relies on the file path being in a specific format (it
> takes the device name returned by FileStore.name() for each data directory
> and looks it up under /sys/block/<device>/queue/read_ahead_kb.).
> This breaks for device-mapper-backed volumes, where FileStore.name() returns
> the device-mapper alias path rather than the real kernel block device. As a
> result, the check just logs a DEBUG-level "No 'read_ahead_kb' setting found”
> message instead of warning the operator.
> The proposed fix finds each disk's real kernel name by checking every
> device’s alias name under /sys/block and making a reverse-lookup map (instead
> of relying on /dev/mapper, which isn't accessible inside the containers where
> this bug occurs).
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