Automate application recovery


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New players
By combining transactional replication and shadow server technologies, a small number of storage vendors are delivering products designed to manage application continuity, rather than just provide fast application recovery; current products (with one exception) are available only for Microsoft Exchange. Vendors with offerings in this space include Cemaphore Systems Inc., Sonasoft Corp. and Teneros Inc.

These companies ship appliances that are preconfigured to be a shadow server for a primary Microsoft Exchange server. The appliance is connected to the network and configured for transactional replication. Appliances can be deployed locally for high availability, in remote configurations for disaster recovery, or in hybrid configurations that can provide disaster recovery and high availability. Some of the offerings also include outsourcing the ongoing management of the shadow server (see "ACC products for Microsoft Exchange," below).

The native transactional replication capabilities inherent in most messaging and database products will stop processing at the source and target sites once a "corrupt" transaction has been identified. While this is important for data integrity, it doesn't support the concept of application continuity. Some of the above products can detect data corruption and fix the problem so that the app can continue to run reliably. Suspect

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transactions are removed from the the source and target logs, and the app is allowed to continue. Repair is attempted, and any transactions that can't be repaired are marked for review by administrators.

There are downsides to these products. First and foremost, since the shadow server will be mirroring the source application, it will contain twice the amount of storage. CCA models leverage a shared-disk store, so they're likely to require far less storage. Disk is relatively cheap, but the requirement for twice the amount of storage will limit the cost-effectiveness of these products, particularly for larger application environments.

ACC products for Microsoft Exchange
MailShadow from Cemaphore Systems Inc. A software-based product designed to run on network-attached Wintel platforms, MailShadow provides a hot standby Exchange server and supports failover at the Active Directory level. Because it uses MAPI to replicate Exchange objects, protection can be configured at the mailbox level (in addition to the entire server) and it can support n-into-one configurations where multiple source mailboxes on multiple Exchange servers can be replicated to a single, centralized Exchange server. MailShadow can also be used to nondisruptively migrate to Exchange 2007.

SonaSafe for Exchange Server from Sonasoft Corp. Deployed as a network-based appliance, SonaSafe is an integrated backup and replication platform that can be used for all Windows-based apps such as Exchange, SQL Server and files. Using MAPI to replicate Exchange objects, SonaSafe supports the ability to protect configurations at the mailbox level. It maintains an active Exchange standby server, providing a platform for fast failover either locally or remotely for Exchange 2000, 2003 and 2007.

Teneros Application Continuity Appliances for Microsoft Exchange from Teneros Inc. Teneros offers managed services for Exchange 2000, 2003 and 2007. The ACA resides at the user's site and is managed remotely by the Teneros Network Operations Center. Transactions are replicated using MAPI (supporting mailbox-level protection) or by directly accessing Exchange log files (for lower overhead on the production Exchange server). Teneros supports full Outlook client functionality in pre- or post-failover modes.

This was first published in April 2008

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