HDFS now includes (shipping in CDH 5.8.2 and later) a comprehensive storage capacity-management approach for moving data across nodes.
In HDFS, the DataNode spreads the data blocks into local filesystem directories, which can be specified using dfs.datanode.data.dir in hdfs-site.xml. In a typical installation, each directory, called a volume in HDFS terminology, is on a different device (for example, on separate HDD and SSD).
When writing new blocks to HDFS,
This new feature gives Hadoop admins the commonplace ability to replace failed DataNode drives without unscheduled downtime.
Hot swapping—the process of replacing system components without shutting down the system—is a common and important operation in modern, production-ready systems. Because disk failures are common in data centers, the ability to hot-swap hard drives is a supported feature in hardware and server operating systems such as Linux and Windows Server,