long startTime = System.currentTimeMillis();
ReplaceBlockHeader replaceBlockHeader =
new ReplaceBlockHeader(versionAndOpcode);
/* read header */
replaceBlockHeader.readFields(in);
int namespaceId = replaceBlockHeader.getNamespaceId();
long blockId = replaceBlockHeader.getBlockId();
long genStamp = replaceBlockHeader.getGenStamp();
Block block = new Block(blockId, dataXceiverServer.estimateBlockSize,
genStamp);