Quest Availability Manager for Exchange
Quest offers QAM (Quest Availability Manager) alone or as part of the Quest Availability Suite. The suite also includes a management application that proactively monitors Exchange, looking for data errors or configuration errors that might cause problems. I tested the management product, Quest Spotlight on Exchange, earlier this year.
QAM -- Version 2.0 in this review -- works in a fashion similar to MailShadow, allowing the administrator to designate specific mailboxes to be protected and moving users to a reserve server if any of the protected Exchange servers becomes unavailable. As does MailShadow, QAM replicates transactions rather than duplicating the message store, so it is not vulnerable to replicating database problems, and one backup server can protect multiple primary Exchange servers.
As opposed to MailShadow, QAM does use an agent on the server, but it offers additional benefits, including automatic fail-over from the primary to the secondary mailbox store. Another advantage is lower pricing per mailbox than MailShadow.
Installation of QAM involves the agent and an extension to the Microsoft Exchange System Management application to allow it to manage the QAM functions as well. In addition, you must give the Administrator account the proper permissions and set up a service account. Finally, you will need a second mailbox store, which may either be on the same Exchange server as the primary or on a second Exchange server. QAM allows you to set up secondary stores on two Exchange servers so that each fails over to the other, or to set up a backup Exchange server with stores for each primary Exchange server in the enterprise.
If QAM detects a failure on the primary Exchange server, either in the availability of the store or in Exchange services, it will initiate fail-over to the secondary store. Users will have to restart Outlook to switch to the secondary store, and QAM provides an alert notifying them of this. It takes about five minutes for the fail-over process to take place, during which users cannot access their accounts, although incoming messages are still received by the backup Exchange server.
When the administrator shifts mailboxes back to the primary Exchange server, all changes made to the secondary server are replicated back to the primary.
Quest offers a variety of applications to make managing Exchange easier, including a monitoring/troubleshooting application, migration managers to ease the transition from older versions of Exchange to newer ones, and more. Tight integration among these applications makes overall management easier and can also help prevent problems such as mailbox store corruption from happening in the first place. Given the low cost of $8 per mailbox ($10 per mailbox for the suite), Quest Availability Manager is easy to recommend to any administrator who can live with a five-minute delay in availability of e-mail for end-users.
Lucid8 DigiVault
DigiVault is a backup product, not a fail-over system, but because it provides continuous data protection, it has a place in the high-availability scenario. It uses a small agent on each Exchange 2000 or Exchange 2003 server to track all changes to the database. All transactions are recorded as they occur, ensuring no loss of e-mails that have arrived since the last backup. I tested Version 1.4.
Multiple Exchange servers can be protected by one DigiVault repository and be managed from a single console. Backups can be scheduled, but restores are performed manually.
DigiVault requires domain admin privileges to install. The console and the DigiStore vault can share the same system. The DigiStore repository requires enough storage to hold the mail stores for all servers you want to protect. Although the repository is compressed, storage requirements will quickly mount if you keep each version of messages in the store. Archiving can be driven by fine-grain policies, but policy is applied on a per-store basis. You can track every change to some accounts, while keeping only the latest copy of other mailboxes, but only by spreading the accounts across separate stores.