hdfs-

1、在属性dfs.namenode.name.dir指定的目录中创建相应的元数据文件

a)current/VERSION

#Fri Dec 06 11:21:35 CST 2013
namespaceID=140437801
clusterID=CID-5a02557f-1977-44d6-b7bc-d124be2d0ba3
cTime=0
storageType=NAME_NODE
blockpoolID=BP-599437854-10.12.120.79-1386299958223
layoutVersion=-47

b)current/seen_txid
写入事务序号txid

0

FSImage$FSImageSaver写入current/fsimage.ckpt
然后再重命名为fsimage(+19位的txid)fsimage_0000000000000000000
1、文件头

out.writeInt(HdfsConstants.LAYOUT_VERSION);
out.writeInt(sourceNamesystem.unprotectedGetNamespaceInfo()
            .getNamespaceID());
out.writeLong(fsDir.rootDir.numItemsInTree());//整个文件系统中包含有多少文件和目录
out.writeLong(sourceNamesystem.getGenerationStampV1());
out.writeLong(sourceNamesystem.getGenerationStampV2());       out.writeLong(sourceNamesystem.getGenerationStampAtblockIdSwitch());
out.writeLong(sourceNamesystem.getLastAllocatedBlockId());
out.writeLong(context.getTxId());
out.writeLong(sourceNamesystem.getLastInodeId());

2、接下来便是目录和文件的元数据信息

Map<String, INodeFileUnderConstruction> nodes =
          leaseManager.getINodesUnderConstruction();
      out.writeInt(nodes.size()); // write the size    
      for (Map.Entry<String, INodeFileUnderConstruction> entry
           : nodes.entrySet()) {
        FSImageSerialization.writeINodeUnderConstruction(
            out, entry.getValue(), entry.getKey());
writeString(path, out);
    out.writeLong(cons.getId());
    out.writeShort(cons.getFileReplication());
    out.writeLong(cons.getModificationTime());
    out.writeLong(cons.getPreferredBlockSize());

    writeBlocks(cons.getBlocks(), out);
    cons.getPermissionStatus().write(out);

    writeString(cons.getClientName(), out);
    writeString(cons.getClientMachine(), out);

    out.writeInt(0); //  do not store locations of last block


      }

参考：http://abloz.com/2013/01/08/hadoop-1-0-4-fsimage-file-format.html
http://blog.csdn.net/xhh198781/article/details/6904615