Raid常用代码片段备忘

DistributedRaidFileSystem其实就是装饰者设计模式中的装饰者，对DistributedFileSystem进行了封装，关键是DistributedRaidFileSystem.ExtFSDataInputStream.ExtFsInputStream对FSInputStream.read(byte[] b, int offset, int len)封装，捕获BlockMissingException，ChecksumException用unraid恢复。

 

Configuration使用了DistributedRaidFileSystem，要得到DistributedFileSystem：

    FileSystem fs = (new Path(path)).getFileSystem(conf);
    // if we got a raid fs, get the underlying fs
    if (fs instanceof DistributedRaidFileSystem) {
      fs = ((DistributedRaidFileSystem) fs).getFileSystem();
    }

    // check that we have a distributed fs
    if (!(fs instanceof DistributedFileSystem)) {
      throw new IOException("expected DistributedFileSystem but got " +
                fs.getClass().getName());
    }

    final DistributedFileSystem dfs = (DistributedFileSystem) fs;