HDFS-17936. Detect slow disks separately by storage type#8558
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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.
public V chooseVolume(List<V> volumes, long replicaSize, String storageId) throws IOException { if (volumes.size() < 1) { throw new DiskOutOfSpaceException("No more available volumes"); } ... }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.