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Because the shadow server runs an active version of the primary application, application software licensing costs will double. CCA architectures require only one active license at any one time, and most cluster vendors give big discounts on the secondary application software license (if it's even required). For small applications, this second application software license may be a minimal expense, but it can become quite onerous for large applications.
As presently constituted, application continuity computing (ACC) is best suited for SMBs, not large enterprises. "We already have at least one of every kind of high-availability product there is, and while ACC offers the same types of fast recovery and support for mainstream applications we already enjoy, it wouldn't be cost-effective for our large data sets," says Steven Hirsch, senior VP of technology at NYSE Euronext.
Smaller customers, on the other hand, responded positively. "I'm a one-man IT shop and am managing over 20 applications," says David Clark, IT director at Jones Waldo, a Salt Lake City law firm. "I've already deployed one of these solutions for Exchange, and I would do it in a heartbeat to handle SQL Server." Hugh Smallwood Jr., CIO at Hagerstown, MD-based Ongoing Operations LLC, a business continuity provider for credit unions, agrees that the simplicity of the model is one of the primary reasons for deployment.
| believe that a recovery strategy based on log replication has significant advantages over traditional shared-disk clustering, and we consciously built native support for this model into Exchange 2007 with features like CCR," says Perry Clarke, product unit manager for Microsoft Exchange Server. "The simplicity of this model makes it appealing not only for SMBs, but also for larger enterprises."
While today's ACC products are focused exclusively on Exchange, this will likely change over the next year. Several ACC vendors say they'll support SQL Server and SharePoint in the future. It's somewhat surprising that an Oracle-based product isn't yet available, but that's also likely to change in the next year. ACC vendors wouldn't talk about specific product roadmaps, but natural extensions would include better integration with other secondary data management functions such as enterprise backup (for visibility within backup catalogs), ediscovery, archiving, data classification, information tiering and destruction.
ACC isn't a replacement for backup and restore, which must still be done on a regular basis to provide for file-level and other partial restore requirements. What it does offer is advantages in the data protection arena by allowing users to offload backup operations to the shadow server. "Do-it-yourself" approaches offering similar application recovery capabilities are available, but they clearly require more sophisticated administrative expertise and, as such, are likely to have higher management costs over time. In the mid and lower range, ACC is an attractive alternative to solutions like FTC, CCA and other approaches targeted at automating application recovery.
This was first published in April 2008