caozhiqiang created HDFS-17936:
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             Summary: Detect slow disks separately by storage type
                 Key: HDFS-17936
                 URL: https://issues.apache.org/jira/browse/HDFS-17936
             Project: Hadoop HDFS
          Issue Type: Bug
    Affects Versions: 3.6.0
            Reporter: caozhiqiang
            Assignee: caozhiqiang


The current slow disk detection does not differentiate between storage types. 
When a DataNode has 1 SSD and 10 HDDs with 
dfs.datanode.max.slowdisks.to.exclude=2 and
dfs.datanode.min.outlier.detection.disks=5, if the SSD is under heavy 
read/write load, the single SSD may be identified as a slow disk. Client tasks 
writing SSD data to that DataNode will then fail to select a volume and report: 
No more available volumes.
{code:java}
public V chooseVolume(List<V> volumes, long replicaSize, String storageId)
    throws IOException {
  if (volumes.size() < 1) {
    throw new DiskOutOfSpaceException("No more available volumes");
  }
...
} {code}
Therefore, slow disk detection should be performed separately for each storage 
type. If the number of disks of a given storage type is less than 
dfs.datanode.min.outlier.detection.disks, detection for that storage type is 
skipped entirely.



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