13 min read

Microsoft SQL Server 2008 High Availability

Microsoft SQL Server 2008 High Availability

Minimize downtime, speed up recovery, and achieve the highest level of availability and reliability for SQL server applications by mastering the concepts of database mirroring,log shipping,clustering, and replication

  •  Install various SQL Server High Availability options in a step-by-step manner
  •  A guide to SQL Server High Availability for DBA aspirants, proficient developers and system administrators
  •  Learn the pre and post installation concepts and common issues you come across while working on SQL Server High Availability
  •  Tips to enhance performance with SQL Server High Availability
  •  External references for further study 

Windows domains and domain users

In the early era of Windows, operating system user were created standalone until Windows NT operating system hit the market. Windows NT, that is, Windows New Technology introduced some great feature to the world—including domains.

A domain is a group of computers that run on Windows operating systems. Amongst them is a computer that holds all the information related to user authentication and user database and is called the domain controller (server), whereas every user who is part of this user database on the domain controller is called a domain user. Domain users have access to any resource across the domain and its subdomains with the privilege they have, unlike the standalone user who has access to the resources available to a specific system.

With the release of Windows Server 2000, Microsoft released Active Directory (AD), which is now widely used with Windows operating system networks to store, authenticate, and control users who are part of the domain. A Windows domain uses various modes to authenticate users—encrypted passwords, various handshake methods such as PKI, Kerberos, EAP, SSL certificates, NAP, LDAP, and IP Sec policy—and makes it robust authentication. One can choose the authentication method that suits business needs and based on the environment.

Let’s now see various authentication methods in detail.

  • Public Key Infrastructure (PKI): This is the most common method used to transmit data over insecure channels such as the Internet using digital certificates. It has generally two parts—the public and private keys. These keys are generated by a Certificate Authority, such as, Thawte. Public keys are stored in a directory where they are accessible by all parties. The public key is used by the message sender to send encrypted messages, which then can be decrypted using the private key.
  • Kerberos: This is an authentication method used in client server architecture to authorize the client to use service(s) on a server in a network. In this method, when a client sends a request to use a service to a server, a request goes to the authentication server, which will generate a session key and a random value based on the username. This session key and a random value are then passed to the server, which grants or rejects the request. These sessions are for certain time period, which means for that particular amount of time the client can use the service without having to re-authenticate itself.
  • Extensible Authentication Protocol (EAP): This is an authentication protocol generally used in wireless and point-to-point connections.
  • SSL Certificates: A Secure Socket Layer certificate (SSL) is a digital certificate that is used to identify a website or server that provides a service to clients and sends the data in an encrypted form. SSL certificates are typically used by websites such as GMAIL. When we type a URL and press Enter, the web browser sends a request to the web server to identify itself. The web server then sends a copy of its SSL certificate, which is checked by the browser. If the browser trusts the certificate (this is generally done on the basis of the CA and Registration Authority and directory verification), it will send a message back to the server and in reply the web server sends an acknowledgement to the browser to start an encrypted session.
  • Network Access Protection (NAP): This is a new platform introduced by Microsoft with the release of Windows Server 2008. It will provide access to the client, based on the identity of the client, the group it belongs to, and the level compliance it has with the policy defined by the Network Administrators. If the client doesn’t have a required compliance level, NAP has mechanisms to bring the client to the compliance level dynamically and allow it to access the network.
  • Lightweight Directory Access Protocol (LDAP): This is a protocol that runs over TCP/IP directly. It is a set of objects, that is, organizational units, printers, groups, and so on. When the client sends a request for a service, it queries the LDAP server to search for availability of information, and based on that information and level of access, it will provide access to the client.
  • IP Security (IPSEC): IP Security is a set of protocols that provides security at the network layer. IP Sec provides two choices:
    • Authentication Header: Here it encapsulates the authentication of the sender in a header of the network packet.
    • Encapsulating Security Payload: Here it supports encryption of both the header and data.

Now that we know basic information on Windows domains, domain users, and various authentication methods used with Windows servers, I will walk you through some of the basic and preliminary stuff about SQL Server security!

Understanding SQL Server Security

Security!! Now-a-days we store various kinds of information into databases and we just want to be sure that they are secured. Security is the most important word to the IT administrator and vital for everybody who has stored their information in a database as he/she needs to make sure that not a single piece of data should be made available to someone who shouldn’t have access. Because all the information stored in the databases is vital, everyone wants to prevent unauthorized access to highly confidential data and here is how security implementation in SQL Server comes into the picture.

With the release of SQL Server 2000, Microsoft (MS) has introduced some great security features such as authentication roles (fixed server roles and fixed database roles), application roles, various permissions levels, forcing protocol encryption, and so on, which are widely used by administrators to tighten SQL Server security.

Basically, SQL Server security has two paradigms: one is SQL Server’s own set of security measures and other is to integrate them with the domain. SQL Server has two methods of authentication.

Windows authentication

In Windows authentication mode, we can integrate domain accounts to authenticate users, and based on the group they are members of and level of access they have, DBAs can provide them access on the particular SQL server box.

Whenever a user tries to access the SQL Server, his/her account is validated by the domain controller first, and then based on the permission it has, the domain controller allows or rejects the request; here it won’t require separate login ID and password to authenticate. Once the user is authenticated, SQL server will allow access to the user based on the permission it has. These permissions are in form of Roles including Server, fixed DB Roles, and Application roles.

    • Fixed Server Roles: These are security principals that have server-wide scope. Basically, fixed server roles are expected to manage the permissions at server level. We can add SQL logins, domain accounts, and domain groups to these roles. There are different roles that we can assign to a login, domain account, or group—the following table lists them.

      Microsoft SQL Server 2008 High Availability

    • Fixed DB Roles: These are the roles that are assigned to a particular login for the particular database; its scope is limited to the database it has permission to. There are various fixed database roles, including the ones shown in the following table:

Microsoft SQL Server 2008 High Availability

  • Application Role: The Application role is a database principal that is widely used to assign user permissions for an application. For example, in a home-grown ERP, some users require only to view the data; we can create a role and add a db_datareader permission to it and then can add all those users who require read-only permission.
  • Mixed Authentication: In the Mixed authentication mode, logins can be authenticated by the Windows domain controller or by SQL Server itself. DBAs can create logins with passwords in SQL Server. With the release of SQL Server 2005, MS has introduced password policies for SQL Server logins. Mixed mode authentication is used when one has to run a legacy application and it is not on the domain network.

In my opinion, Windows authentication is good because we can use various handshake methods such as PKI, Kerberos, EAP, SSL NAP, LDAP, or IPSEC to tighten the security.

SQL Server 2005 has enhancements in its security mechanisms. The most important features amongst them are password policy, native encryption, separation of users and schema, and no need to provide system administrator (SA) rights to run profiler.

These are good things because SA is the super user, and with the power this account has, a user can do anything on the SQL box, including:

  • The user can grant ALTER TRACE permission to users who require to run profiler
  • The user can create login and users
  • The user can grant or revoke permission to other users

A schema is an object container that is owned by a user and is transferable to any other users. In earlier versions, objects are owned by users, so if the user leaves the company we cannot delete his/her account from the SQL box just because there is some object he/she has created. We first have to change the owner of that object and then we can delete that account. On the other hand, in the case of a schema, we could have dropped the user account because the object is owned by the schema.

Now, SQL Server 2008 will give you more control over the configuration of security mechanisms. It allows you to configure metadata access, execution context, and auditing events using DDL triggers—the most powerful feature to audit any DDL event.

If one wishes to know more about what we have seen till now, he/she can go through the following links:

In this section, we understood the basics of domains, domain users, and SQL Server security. We also learned why security is given so much emphasize these days.

In the next section, we will understand the basics of clustering and its components.

What is clustering?

Before starting with SQL Server clustering, let’s have a look at clustering in general and Windows clusters.

The word Cluster itself is self-descriptive—a bunch or group. When two or more than two computers are connected to each other by means of a network and share some of the common resources to provide redundancy or performance improvement, they are known as a cluster of computers.

Clustering is usually deployed when there is a critical business application running that needs to be available 24 X 7 or in terminology—High Availability. These clusters are known as Failover clusters because the primary goal to set up the cluster is to make services or business processes that are business critical available 24 X 7. MS Windows server Enterprise and Datacenter edition supports failover clustering. This is achieved by having two identical nodes connected to each other by means of private network or commonly used resources. In case of failure of any common resource or services, the first node (Active) passes the ownership to another node (Passive).

SQL Server Clustering is built on top of Windows Clustering, which means before we go about installing SQL Server clustering, we should have Windows clustering installed. Before we start, let’s understand the commonly used shared resources for the cluster server.

Clusters with 2, 4, 8, 12 or 32 nodes can be built Windows Server 2008 R2. Clusters are categorized in the following manner:

    • High-Availability Clusters: This type of cluster is known as a Failover cluster. High Availability clusters are implemented when the purpose is to provide highly available services. For implementing a failover or high availability cluster one may have up to 16 nodes in a Microsoft Cluster. Clustering in Windows operating systems was first introduced with the release of Windows NT 4.0 Enterprise Edition, and was enhanced gradually. Even though we can have non-identical hardware, we should use identical hardware. This is because if the node to which cluster fails over has lower configuration, then we might face degradation in performance.

      Microsoft SQL Server 2008 High Availability

    • Load Balancing: This is the second form of cluster that can be configured. This type of cluster can be configured by linking multiple computers with each other and making use of each resource they need for operation. From the user’s point of view, all of these servers/nodes linked to each other are different. However, it is collectively and virtually a single system, with the main goal being to balance work by sharing CPU, disk, and every possible resource among the linked nodes and that is why it is known as a Load Balancing cluster.

SQL Server doesn’t support this form of clustering.

  • Compute Clusters: When computers are linked together with the purpose of using them for simulation for aircraft, they are known as a compute cluster. A well-known example is Beowulf computers.
  • Grid Computing: This is one kind of clustering solution, but it is more often used when there is a dispersed location. This kind of cluster is called a Supercomputer or HPC. The main application is scientific research, academic, mathematical, or weather forecasting where lots of CPUs and disks are required—SETI@home is a well-known example. If we talk about SQL Server clusters, there are some cool new features that are added in the latest release of SQL Server 2008, although with the limitation that these features are available only if SQL Server 2008 is used with Windows Server 2008. So, let’s have a glance at these features:
    • Service SID: Service SIDs were introduced with Windows Vista and Windows Server 2008. They enable us to bind permissions directly to Windows services. In the earlier version of SQL Server 2005, we need to have a SQL Server Services account that is a member of a domain group so that it can have all the required permissions. This is not the case with SQL Server 2008 and we may choose Service SIDs to bypass the need to provision domain groups.
    • Support for 16 nodes: We may add up to 16 nodes in our SQL Server 2008 cluster with SQL Server 2008 Enterprise 64-bit edition.
    • New cluster validation: As a part of the installation steps, a new cluster validation step is implemented. Prior to adding a node into an existing cluster, this validation step checks whether or not the cluster environment is compatible.
    • Mount Drives: Drive letters are no longer essential. If we have a cluster configured that has limited drive letters available, we may mount a drive and use it in our cluster environment, provided it is associated with the base drive letter.
    • Geographically dispersed cluster node: This is the super-cool feature introduced with SQL Server 2008, which uses VLAN to establish connectivity with other cluster nodes. It breaks the limitation of having all clustered nodes at a single location.
    • IPv6 Support: SQL Server 2008 natively supports IPv6, which increases network IP address size to 128 bit from 32 bit.
    • DHCP Support: Windows server 2008 clustering introduced the use of DHCP-assigned IP addresses by the cluster services and it is supported by SQL Server 2008 clusters. It is recommended to use static IP addresses. This is because if some of our application depends on IP addresses, or in case of failure of renewing IP address from DHCP server, there would be a failure of IP address resources.
    • iSCSI Support: Windows server 2008 supports iSCSI to be used as storage connection; in earlier versions, only SAN and fibre channels were supported.

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