Overview
OSD Max Scrubs (osd_max_scrubs) is a Ceph configuration parameter that defines how many simultaneous scrub operations an OSD can perform. Scrubbing is Ceph’s data integrity checking mechanism that verifies the consistency of stored data.
Default Configuration
- Default value: 3 concurrent scrubs per OSD
- This default is optimized for SSD-based clusters
- For HDD-based clusters, this value should be reduced to 1
Performance Impact
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HDD Characteristics
- HDDs are mechanical devices with physical seek times
- Concurrent scrubs cause random I/O patterns
- Multiple seeks significantly degrade HDD performance
- Sequential operations are preferred for HDDs
-
SSD Characteristics
- No mechanical movement
- Better handling of parallel operations
- Can sustain multiple concurrent scrubs without significant performance impact
Configuration Recommendation
For HDD-based clusters:
ceph config set osd osd_max_scrubs 1