HDFS Snapshots
Snapshots功能非常重要，可以保证HDFS在出现异常情况时可以进行恢复。 Snapshots可以使用在整个HDFS系统上，也可以只对其中的部分文件目录。
HDFS Snapshots are read-only point-in-time copies of file system. Snapshots can be taken on a subtree of the file system or the entire file system.
The HDFS path should be Snapshottable.
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| Snapshots Paths “.snapshot” is used for accessing its snapshots. hadoop fs -ls /foo/.snapshot Allow Snapshots command: hdfs dfsadmin -allowSnapshot <path> Disallow Snapshots command: hdfs dfsadmin -disallowSnapshot <path> Create Snapshots command: hdfs dfs -createSnapshot <path> [<snapshotName>] Delete Snapshots command: hdfs dfs -deleteSnapshot <path> [<snapshotName>] Rename Snapshots command: hdfs dfs -renameSnapshot <path> <oldName> <newName> Get Snapshottable Directory Listing command: hdfs lsSnapshottableDir Get Snapshots Difference Report command: hdfs snapshotDiff <path> <fromSnapshot> <toSnapshot>
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