如果把一个641MB的上传到hadoop的文件系统 中，如果hdfs副本数设为3，则在datanodes中 会新增多少block

首先需要确定该文件的block大小，Hadoop默认的block大小为128MB，因此641MB的文件将被分成5个block，其中前4个block大小为128MB，最后一个block大小为109MB。

如果HDFS副本数为3，则每个block都会被复制两次，因此总共会有15个block，其中5个原始block和10个副本block。每个datanode上的block数量取决于HDFS的块放置策略。如果使用默认的块放置策略，则每个datanode上会分别存储5个block和10个副本block。

相关问题

hadoop Starting datanodes

When starting a Hadoop cluster, one of the critical steps is to start the datanodes. Datanodes are responsible for storing and managing the actual data in the Hadoop Distributed File System (HDFS).

To start the datanodes, you need to follow these steps:

1. Ensure that Hadoop is installed and configured correctly on all the nodes in the cluster.
2. Start the Hadoop daemons on the namenode machine by running the command `start-dfs.sh`.
3. Start the datanodes by running the command `start-dfs.sh datanode`.
4. Verify that the datanodes have started correctly by checking the logs and the Hadoop web interface.

Once the datanodes are up and running, they will begin to communicate with the namenode and start storing the data in the HDFS.

再提供一个hdfs dfsadmin全量命令测试脚本

下面是一个HDFS `dfsadmin` 全量命令测试脚本的示例：

#!/bin/bash

# Set variables
HDFS_USER=hdfs
HDFS_COMMAND=/usr/local/hadoop/bin/hdfs
NAMENODE_HOST=localhost

# Check if HDFS is running
$HDFS_COMMAND dfsadmin -report >/dev/null 2>&1
if [ $? -eq 0 ]; then
  echo "HDFS is running"
else
  echo "HDFS is not running"
  exit 1
fi

# Check if HDFS user has permissions
su $HDFS_USER -c "$HDFS_COMMAND dfsadmin -report" >/dev/null 2>&1
if [ $? -eq 0 ]; then
  echo "HDFS user has permissions"
else
  echo "HDFS user does not have permissions"
  exit 1
fi

# Check if namenode is active
$HDFS_COMMAND dfsadmin -report | grep -A1 "Name:" | grep "$NAMENODE_HOST:8020" >/dev/null 2>&1
if [ $? -eq 0 ]; then
  echo "Namenode is active"
else
  echo "Namenode is not active"
  exit 1
fi

# Check if all datanodes are active
$HDFS_COMMAND dfsadmin -report | grep "Datanodes available:" >/dev/null 2>&1
if [ $? -eq 0 ]; then
  echo "All datanodes are active"
else
  echo "Not all datanodes are active"
  exit 1
fi

# Check if all blocks are replicated
$HDFS_COMMAND dfsadmin -report | grep "Under replicated blocks:" >/dev/null 2>&1
if [ $? -eq 0 ]; then
  echo "All blocks are replicated"
else
  echo "Not all blocks are replicated"
  exit 1
fi

echo "HDFS is healthy"
exit 0

这个脚本将检查HDFS是否正在运行，HDFS用户是否有权限，namenode是否处于活动状态，所有datanode是否处于活动状态以及所有块是否被复制。如果所有检查都通过，脚本将输出"HDFS is healthy"，否则将输出错误消息并退出。