StorageInfo是NameNode，DataNode 和JNStorage Storage的基类，其包含6个比较重要的字段：
public int layoutVersion; // namenode和datanode怎么在磁盘上存储信息的布局版本号
public int namespaceID; //文件系统的ID
public String clusterID; // 集群的ID
public long cTime; // 文件系统创建的时间
protected final NodeType storageType; // 存储的类型,为（NAMENODE,DATANODE,JOURNAL_NODE）三种
protected static final String STORAGE_FILE_VERSION = "VERSION";
namespaceID：
此值是namenode执行format命令的时候分配的值，为一个int值，为一个非零的随机数，以后不会发生变化，当datanodes注册的时候，他们会收到namespaceID作为注册id，当每次datanode与namenode通信的时候，namenode都会检查此值，如果不认识此id，将会被拒绝。namespaceID被所有文件系统的组件所共享。
此值是有namenode在NNStorage（继承之StorageInfo）类中生成的，具体的生成方法如下：
private static int newNamespaceID() {
int newID = 0;
while(newID == 0)
newID = DFSUtil.getRandom().nextInt(0x7FFFFFFF); // use 31 bits only
return newID;
}
clusterID：
clusterID的生成方式为：CID+一个随机的UUID
public static String newClusterID() {
return "CID-" + UUID.randomUUID().toString();
}
layoutVersion：
在format的时候，来之NameNodeLayoutVersion的EDITLOG_LENGTH(-56, "Add length field to every edit log op");，所以目前固定值为-56
LayoutVersion：
/**
* Enums for features that change the layout version before rolling
* upgrade is supported.
* <br><br>
* To add a new layout version:
* <ul>
* <li>Define a new enum constant with a short enum name, the new layout version
* and description of the added feature.</li>
* <li>When adding a layout version with an ancestor that is not same as
* its immediate predecessor, use the constructor where a specific ancestor
* can be passed.
* </li>
* </ul>
*/
public static enum Feature implements LayoutFeature {
NAMESPACE_QUOTA(-16, "Support for namespace quotas"),
FILE_ACCESS_TIME(-17, "Support for access time on files"),
DISKSPACE_QUOTA(-18, "Support for disk space quotas"),
STICKY_BIT(-19, "Support for sticky bits"),
APPEND_RBW_DIR(-20, "Datanode has \"rbw\" subdirectory for append"),
ATOMIC_RENAME(-21, "Support for atomic rename"),
CONCAT(-22, "Support for concat operation"),
SYMLINKS(-23, "Support for symbolic links"),
DELEGATION_TOKEN(-24, "Support for delegation tokens for security"),
FSIMAGE_COMPRESSION(-25, "Support for fsimage compression"),
FSIMAGE_CHECKSUM(-26, "Support checksum for fsimage"),
REMOVE_REL13_DISK_LAYOUT_SUPPORT(-27, "Remove support for 0.13 disk layout"),
EDITS_CHESKUM(-28, "Support checksum for editlog"),
UNUSED(-29, "Skipped version"),
FSIMAGE_NAME_OPTIMIZATION(-30, "Store only last part of path in fsimage"),
RESERVED_REL20_203(-31, -19, "Reserved for release 0.20.203", true,
DELEGATION_TOKEN),
RESERVED_REL20_204(-32, -31, "Reserved for release 0.20.204", true),
RESERVED_REL22(-33, -27, "Reserved for release 0.22", true),
RESERVED_REL23(-34, -30, "Reserved for release 0.23", true),
FEDERATION(-35, "Support for namenode federation"),
LEASE_REASSIGNMENT(-36, "Support for persisting lease holder reassignment"),
STORED_TXIDS(-37, "Transaction IDs are stored in edits log and image files"),
TXID_BASED_LAYOUT(-38, "File names in NN Storage are based on transaction IDs"),
EDITLOG_OP_OPTIMIZATION(-39,
"Use LongWritable and ShortWritable directly instead of ArrayWritable of UTF8"),
OPTIMIZE_PERSIST_BLOCKS(-40,
"Serialize block lists with delta-encoded variable length ints, " +
"add OP_UPDATE_BLOCKS"),
RESERVED_REL1_2_0(-41, -32, "Reserved for release 1.2.0", true, CONCAT),
ADD_INODE_ID(-42, -40, "Assign a unique inode id for each inode", false),
SNAPSHOT(-43, "Support for snapshot feature"),
RESERVED_REL1_3_0(-44, -41,
"Reserved for release 1.3.0", true, ADD_INODE_ID, SNAPSHOT),
OPTIMIZE_SNAPSHOT_INODES(-45, -43,
"Reduce snapshot inode memory footprint", false),
SEQUENTIAL_BLOCK_ID(-46, "Allocate block IDs sequentially and store " +
"block IDs in the edits log and image files"),
EDITLOG_SUPPORT_RETRYCACHE(-47, "Record ClientId and CallId in editlog to "
+ "enable rebuilding retry cache in case of HA failover"),
EDITLOG_ADD_BLOCK(-48, "Add new editlog that only records allocation of "
+ "the new block instead of the entire block list"),
ADD_DATANODE_AND_STORAGE_UUIDS(-49, "Replace StorageID with DatanodeUuid."
+ " Use distinct StorageUuid per storage directory."),
ADD_LAYOUT_FLAGS(-50, "Add support for layout flags."),
CACHING(-51, "Support for cache pools and path-based caching"),
// Hadoop 2.4.0
PROTOBUF_FORMAT(-52, "Use protobuf to serialize FSImage"),
EXTENDED_ACL(-53, "Extended ACL"),
RESERVED_REL2_4_0(-54, -51, "Reserved for release 2.4.0", true,
PROTOBUF_FORMAT, EXTENDED_ACL);
NameNodeLayoutVersion：
ROLLING_UPGRADE(-55, -53, "Support rolling upgrade", false),
EDITLOG_LENGTH(-56, "Add length field to every edit log op");
DataNodeLayoutVersion：
FIRST_LAYOUT(-55, -53, "First datenode layout", false);
cTime：
目前为0
storageType：
目前分为
NAME_NODE,
DATA_NODE,
JOURNAL_NODE;
三个值。
STORAGE_FILE_VERSION：
上面的几个字段保存的文件名称，目前为VERSION
VERSION文件内容例如：
#Fri Jul 18 15:31:08 CST 2014
namespaceID=2137650844
clusterID=CID-87f4e5d6-8a7a-45da-a6a6-eba8ffecbebb
cTime=0
storageType=NAME_NODE
blockpoolID=BP-1028050584-192.168.1.110-1405668065552
layoutVersion=-56
源代码：
public class StorageInfo {
public int layoutVersion; // layout version of the storage data
public int namespaceID; // id of the file system
public String clusterID; // id of the cluster
public long cTime; // creation time of the file system state
protected final NodeType storageType; // Type of the node using this storage
protected static final String STORAGE_FILE_VERSION = "VERSION";
public StorageInfo(NodeType type) {
this(0, 0, "", 0L, type);
}
public StorageInfo(int layoutV, int nsID, String cid, long cT, NodeType type) {
layoutVersion = layoutV;
clusterID = cid;
namespaceID = nsID;
cTime = cT;
storageType = type;
}
public StorageInfo(StorageInfo from) {
this(from.layoutVersion, from.namespaceID, from.clusterID, from.cTime,
from.storageType);
}
/**
* Layout version of the storage data.
*/
public int getLayoutVersion(){ return layoutVersion; }
/**
* Namespace id of the file system.<p>
* Assigned to the file system at formatting and never changes after that.
* Shared by all file system components.
*/
public int getNamespaceID() { return namespaceID; }
/**
* cluster id of the file system.<p>
*/
public String getClusterID() { return clusterID; }
/**
* Creation time of the file system state.<p>
* Modified during upgrades.
*/
public long getCTime() { return cTime; }
public void setStorageInfo(StorageInfo from) {
layoutVersion = from.layoutVersion;
clusterID = from.clusterID;
namespaceID = from.namespaceID;
cTime = from.cTime;
}
public boolean versionSupportsFederation(
Map<Integer, SortedSet<LayoutFeature>> map) {
return LayoutVersion.supports(map, LayoutVersion.Feature.FEDERATION,
layoutVersion);
}
@Override
public String toString() {
StringBuilder sb = new StringBuilder();
sb.append("lv=").append(layoutVersion).append(";cid=").append(clusterID)
.append(";nsid=").append(namespaceID).append(";c=").append(cTime);
return sb.toString();
}
public String toColonSeparatedString() {
return Joiner.on(":").join(
layoutVersion, namespaceID, cTime, clusterID);
}
/**
* Get common storage fields.
* Should be overloaded if additional fields need to be get.
*
* @param props
* @throws IOException
*/
protected void setFieldsFromProperties(
Properties props, StorageDirectory sd) throws IOException {
setLayoutVersion(props, sd);
setNamespaceID(props, sd);
setcTime(props, sd);
setClusterId(props, layoutVersion, sd);
checkStorageType(props, sd);
}
/** Validate and set storage type from {@link Properties}*/
protected void checkStorageType(Properties props, StorageDirectory sd)
throws InconsistentFSStateException {
if (storageType == null) { //don't care about storage type
return;
}
NodeType type = NodeType.valueOf(getProperty(props, sd, "storageType"));
if (!storageType.equals(type)) {
throw new InconsistentFSStateException(sd.root,
"Incompatible node types: storageType=" + storageType
+ " but StorageDirectory type=" + type);
}
}
/** Validate and set ctime from {@link Properties}*/
protected void setcTime(Properties props, StorageDirectory sd)
throws InconsistentFSStateException {
cTime = Long.parseLong(getProperty(props, sd, "cTime"));
}
/** Validate and set clusterId from {@link Properties}*/
protected void setClusterId(Properties props, int layoutVersion,
StorageDirectory sd) throws InconsistentFSStateException {
// Set cluster ID in version that supports federation
if (LayoutVersion.supports(getServiceLayoutFeatureMap(),
Feature.FEDERATION, layoutVersion)) {
String cid = getProperty(props, sd, "clusterID");
if (!(clusterID.equals("") || cid.equals("") || clusterID.equals(cid))) {
throw new InconsistentFSStateException(sd.getRoot(),
"cluster Id is incompatible with others.");
}
clusterID = cid;
}
}
/** Validate and set layout version from {@link Properties}*/
protected void setLayoutVersion(Properties props, StorageDirectory sd)
throws IncorrectVersionException, InconsistentFSStateException {
int lv = Integer.parseInt(getProperty(props, sd, "layoutVersion"));
if (lv < getServiceLayoutVersion()) { // future version
throw new IncorrectVersionException(getServiceLayoutVersion(), lv,
"storage directory " + sd.root.getAbsolutePath());
}
layoutVersion = lv;
}
/** Validate and set namespaceID version from {@link Properties}*/
protected void setNamespaceID(Properties props, StorageDirectory sd)
throws InconsistentFSStateException {
int nsId = Integer.parseInt(getProperty(props, sd, "namespaceID"));
if (namespaceID != 0 && nsId != 0 && namespaceID != nsId) {
throw new InconsistentFSStateException(sd.root,
"namespaceID is incompatible with others.");
}
namespaceID = nsId;
}
public int getServiceLayoutVersion() {
return storageType == NodeType.DATA_NODE ? HdfsConstants.DATANODE_LAYOUT_VERSION
: HdfsConstants.NAMENODE_LAYOUT_VERSION;
}
public Map<Integer, SortedSet<LayoutFeature>> getServiceLayoutFeatureMap() {
return storageType == NodeType.DATA_NODE? DataNodeLayoutVersion.FEATURES
: NameNodeLayoutVersion.FEATURES;
}
protected static String getProperty(Properties props, StorageDirectory sd,
String name) throws InconsistentFSStateException {
String property = props.getProperty(name);
if (property == null) {
throw new InconsistentFSStateException(sd.root, "file "
+ STORAGE_FILE_VERSION + " has " + name + " missing.");
}
return property;
}
public static int getNsIdFromColonSeparatedString(String in) {
return Integer.parseInt(in.split(":")[1]);
}
public static String getClusterIdFromColonSeparatedString(String in) {
return in.split(":")[3];
}
/**
* Read properties from the VERSION file in the given storage directory.
*/
public void readProperties(StorageDirectory sd) throws IOException {
Properties props = readPropertiesFile(sd.getVersionFile());
setFieldsFromProperties(props, sd);
}
/**
* Read properties from the the previous/VERSION file in the given storage directory.
*/
public void readPreviousVersionProperties(StorageDirectory sd)
throws IOException {
Properties props = readPropertiesFile(sd.getPreviousVersionFile());
setFieldsFromProperties(props, sd);
}
public static Properties readPropertiesFile(File from) throws IOException {
RandomAccessFile file = new RandomAccessFile(from, "rws");
FileInputStream in = null;
Properties props = new Properties();
try {
in = new FileInputStream(file.getFD());
file.seek(0);
props.load(in);
} finally {
if (in != null) {
in.close();
}
file.close();
}
return props;
}
}