We continue with a detailed study of Microsoft Azure stack as inferred from an introduction of Azure by Microsoft. We reviewed some more features of Azure storage.
The IaaS offerings from Azure storage services include disks and files where as the PaaS offerings from Azure storage services include objects, tables and queues. The storage offerings are built on a unified distributed storage system with guarantees for durability, encryption at Rest, strongly consistent replication, fault tolerance and auto load balancing.
 The redundancy features are handled by storage stamps and a location service. A storage stamp is a cluster of N racks of storage nodes, where each rack is built out as a separate fault domain with redundant networking and power.  Each storage stamp is located by a VIP  and served by layers of Front-Ends, partition layer and stream layer that provides intra stamp replication.The intra stamp provides synchronous replication in the stream layer and ensures that the data is made durable within the storage stamp. The interstamp replication provides asynchronous replication and is focused on replicating data across stamps. We were looking at Blocks, Extents and Streams, the Stream Manager and the Extent Nodes.
The Stream Layer is protected from malicious threats by the data center, Fabric Controller and Windows Azure Storage WAS service. Faults ranging from disk and node errors to power failures, network issues, bit flip and random hardware-failures and software bugs all may result in data corruption. They are prevented by the same block checksums mentioned earlier. 
The replication flow proceeds like this. The Stream Manager assigns three replicas for the first extent (one primary and two secondary) to three extent nodes. They are chosen at random to spread the replicas across different fault and ugprade domains while considering extent node usage for load balancing. The primary is the main replica. All writes go to the primary. The primary then co-ordinates the writes to the secondary.  The primary EN and the location of the three replicas don't change when it is appended and until sealed. When the SM allocates the extent, the extent locations is sent back to the clients. When the last extent becomes sealed, another now becomes the last extent and all new appends become the last extent in the stream. 
If there are multiple outstanding appends to the same extent, the primary EN will respond success in the order of their offset to the clients. The last append position is considered to be the current commit length of the replica.
#codingexercise
Convert a binary tree to a binary search tree
Node ToBSTFromBT(Node root)
{
if (root == null) return root;
var items = ToList(root);
items.sort()
return ToBSTFromInOrder(items);
}
Node toList(node root)
{
If (root == null) return root;
If (root.left != null)
{
var left = toList(root.left);
for( ; left.right != null; left = left.right);
Left.right = root;
}
If (root.right != null)
{
var right = toList(root);
for(; right.left != null; right = right.left);
root.right = right;
}
Return root;
}

Node SortedListToBST(List<int> num, int start, int end, Node root)
{

int mid;

if ( (start + end) %2 == 0)
     mid = (start + end ) / 2 + 1;
else
    mid = (start + end) / 2

var node = new Node();
node.data = num[mid];

if (root != null)
if (num[mid] < root.data)
     root.left = node;
else
    root.right = node

node.left = SortedListToBST(num, start, mid-1, node);

node.right = SortedListToBST(num, mid + 1, end, node);

return node;


};