The price differential between Microsoft SQL Server 2012 Standard Edition and Enterprise Edition (Enterprise costs roughly four times more) makes value becomes a critical consideration. Enterprise's main selling point is AlwaysOn, a refined form of database mirroring designed to provide remote disaster recovery at a database level. Standard Edition, however, relies on log shipping instead of database mirroring, and the most industry experts consider the latter to be preferable in most cases, cost notwithstanding.
AlwaysOn does, in fact, offer several advantages over log shipping. These include automatic and rapid fail-over protection, automatic client redirection, easier configuration, full-text catalog support, built-in network encryption support, and less bandwidth use with asynchronous propagation. In addition, AlwaysOn improves on database mirroring by permitting the user to combine multiple databases into one unit that can be failed over together. It also permits up to four replicas for a database, whereas traditional database mirroring only allows one. Finally, while mirrored databases are always in a state of recovery that prevents the use of that database while actively mirroring, AlwaysOn can grant read-only access to said database for purposes of reporting and backup.
Even with all of these advantages, three notable cons exist. First, all database mirroring provides both synchronous and asynchronous operation modes; AlwaysOn is no exception. Synchronous roughly translates to high-safety mode, while asynchronous emphasizes performance. Organizations requiring heavy use of asynchronous operation will need to possess fast propagation interval time and bandwidth speed or face the possibility of data loss. Second, as mentioned above, AlwaysOn necessitates the licensing of SQL Server Enterprise Edition at quadruple the cost of the Standard Edition. Third, AlwaysOn requires Windows Server Failover Clustering (WSFC) which is only supported in Windows Server 2008 Enterprise Edition or later editions.
With the possible financial and infrastructure cost of licensing Enterprise Edition, some organizations may consider Standard Edition a viable alternative, provided they understand the limitations and advantages of log shipping. As a means for disaster recovery, it requires more maintenance than AlwaysOn. Log shipping demands manual fail-over and the process can take longer than 30 minutes to complete. Likewise, client redirection and role change require manual input. Weaknesses aside, log shipping provides actual backup files as part of the process and supports multiple secondary databases.
Given the risk involved in the extra expense, businesses may face uncertainty when deciding which version to license. Organizations should consider implementing the full-featured 180-day trial from the Microsoft web site before reaching a final decision. Generally speaking, database mirroring is preferable to log shipping, and AlwaysOn's attempt to improve on it cannot responsibly be ignored.
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