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I am optimizing a Hadoop DataNode on RHEL 7 to improve disk performance for large sequential I/O workloads and considering tuning the Linux block device read-ahead (blockdev --setra).

Current observations:

Device: /dev/sdb .. /dev/sdl
Memory: 256 GB
Disk type: SAS/NVMe

My goal is to maximize sequential read/write throughput on DataNodes and reduce I/O bottlenecks for HDFS block operations.

I want to know:

Is it safe to set blockdev --setra 65536 /dev/sdb (≈32 MB) in production for DataNodes?

Is it safe to set echo 1024 > /sys/block/sdb/queue/nr_requests in production for DataNodes?

Are there any official Hadoop or vendor references recommending this approach?

Any potential side effects to watch for when increasing read-ahead this high?

How do others determine the optimal value for large sequential workloads in HDFS?

I have seen general recommendations to increase read-ahead for sequential workloads in Linux (Red Hat Performance Tuning Guide, Intel Hadoop Optimization papers), but Hadoop documentation doesn’t explicitly state numeric values. I’d like to know if this is a reasonable setting and how to validate it.

Context:

  1. HDFS I/O is dominated by large sequential reads/writes
  2. Want to leverage Linux prefetching to improve disk throughput
  3. Saw general recommendations to increase read-ahead in Linux for sequential workloads (Red Hat Performance Tuning Guide, Intel Hadoop Optimization papers), but Hadoop documentation doesn’t explicitly specify numeric values
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