Octopus by Octopus Technologies

Realtime data mirroring over network connections

Maintaining duplicates of up-to-dateinformation is a key capability for a fault-tolerant (or fault-resilient)environment. One way to implement this capability is to designate a system as ahot backup to one or more primary systems and to mirror information from theprimary system to the target system. If a primary system fails, the targetsystem can replace it without losing data because an exact copy of the primarysystem's crucial information is on the backup.

Mirroring is a powerful and sophisticated capability that you don't expectto find on a couple of diskettes in a shrink-wrapped box. And that capability iswhat makes Octopus such an interesting, and in many ways, unique product.

Octopus is a realtime data mirroring software product that OctopusTechnologies developed and markets. The product runs on all NT platforms (Intel,MIPS, Alpha, and PowerPC), operates under both NT Server and Workstation (andWindows 95), with any type of network connection--even wide-area RAS links--tocarry the mirrored information from one system to another. Octopus can mirrordata from one system to another, from several systems to one system, or from onesystem to several. Two systems can even mirror and thus back up each other. Allthese features make Octopus a flexible product for a variety of mirroringstrategies.

Speed is the feature that makes Octopus impressive. It tracks updates asthey occur and then mirrors just the updated information across the network. Theresult is blazingly fast data delivery; the software delivers updated data to atarget system before you can swivel your head to look. You won't, for example,get the same speed over a RAS link as over a LAN link--but you can expectOctopus to perform well in any LAN environment.

Another benefit is that this product lets you mirror information structuresranging from simple flat files to sophisticated databases such as Microsoft'sSQL Server. In fact, the only type of file access that Octopus Technologiesadmits to not being able to handle is the update access that the Microsoft Writeaccessory program uses. Fortunately, Write is a minor application that doesn'toften find its way into the heart of an enterprisewide business solution.

An Octopus Among Us
I tested Octopus 1.6 (build 147f) on Intel-based systems: a Dell and aMicron configured with NT Server 3.51 and a Toshiba laptop running NTWorkstation 4.0 beta 2. A garden-variety 10Mbit-per-second Ethernet networkinterconnected all the systems; I used no switching hubs or otherspeed-enhancing devices.

Installing Octopus is easy, but you have to reboot to activate it. You mustinstall Octopus on both the primary (source) system and backup (target) systembefore you can configure and use it. With other products, you need to configureonly the primary system; the target system receives the configurationinformation from the primary system.

At a minimum, you must identify the primary system's files and directoriesthat you want to mirror to the target. The product's term for these file anddirectory specifications is data vaults. Screen 1 shows the dialog forentering this information. When you add the information about the target system,you can have Octopus query the network to sniff out all the systems runningOctopus software, or you can enter the target system's name. If you have amedium or large LAN, having Octopus query the network can be time consuming, soenter the target system name manually; Octopus will validate the connectionafter you enter the name.

You can configure multiple specifications to enable one-to-many mirroringor to mirror multiple file sets to one target system. All the data vaults youdefine appear in the lower half of the configuration dialog. You can modify ordelete those specifications. You can also select the network protocol (TCP/IP,NetBEUI, or Internet Packet eXchange--IPX) for transporting mirroredinformation. By default, Octopus uses the system's primary network transport.

After configuration, you're ready to go. When you add a new specification,select the Synchronize option under the Vault pulldown menu. Octopus will verifythat the files on the primary and target system are identical and copy filesthat need refreshing.

After Octopus synchronizes the two systems, the settings of the Mirroringand Forwarding options on the Functions pulldown menu let you determine how toprocess subsequent updates. The Mirroring option must be on if you want Octopusto track information changes in the primary system. The Forwarding optiondetermines whether information changes will immediately go to the target system(Forwarding on) or remain in a local log file (Forwarding off). If you setForwarding off, changes will not go until you turn on the Forwarding on option.Then, all logged changes will go to the target system.

Mirroring and forwarding are completely reliable and extremely fast. WhenOctopus was running, I perceived no performance degradation on either theprimary or target system. The mirroring and forwarding capabilities areimpressive.

For NT Server and NT Workstation, Octopus has two types of packaging andlicensing. The basic package provides only mirroring capabilities. If somethinghappens to the primary system, you must manually restart the target system underthe identity of the primary system, or your users must manually switch theirfile and print connections to the target server. The advanced package includesan Automatic Switch Over (ASO) capability that lets the backup systemautomatically restart and assume the primary system's identity.

The ASO capabilities didn't impress me as much as the mirroring andforwarding. To use ASO, you configure the target system to assume the primarysystem's identity (and optionally the IP address) in case of a primary systemfailure. When you enable ASO, the primary system sends "I'm alive"messages to the target system at regular intervals (usually every 15 seconds).If the target system fails to receive an "I'm alive" message, itqueries the primary system. If that query fails, the target system performs apartial restart so it can assume the identity (the system name) of the primarysystem.

The problem with this approach is that if the target system is aworkstation or server participating in an NT domain (and not the Primary DomainController--PDC--or Backup Domain Controller--BDC), the trust relationshipbetween the backup system and the domain controller is violated: The domaincontroller knows that the system assuming the failed system's identity isn'treally the failed system, so the domain controller won't allow any network-basedlogons to that system. You can get around this limitation by setting up locallogon accounts on the target system, but that pretty much defeats the purpose ofa domain controller in the first place. Octopus claims to have addressed thislimitation in the forthcoming 2.0 release, but I was unable to test that releasebefore press time.

This limitation does not, however, totally invalidate the current ASOoption. ASO is good if you operate in a workgroup environment, if you want toimplement failover from a PDC to a BDC, or if you want to provide a hot backupfor a Web server (in this case the backup system assumes the IP address of theprimary Web server). The bottom line is that you have to analyze your fail-overneeds in light of capabilities and limitations in Octopus and--even moreimportant--test your failover procedure before a real failure occurs.

Octopus comes with a printed manual that forms the basis for most of theonline help information. This manual explains reasonably well how to configureand use the mirroring capabilities, but it falls short in explaining how toeffectively deploy the Octopus ASO option.

An Octopus in Your Network?
Aside from the issues with the ASO option, the benefits of Octopus for datamirroring are enormous. In addition to facilitating one-to-one, one-to-many,many-to-one, or many-to-many mirroring, the product has multiplatformcapabilities that let you mirror across hardware architectures. You can, forexample, mirror data on an Intel-based system to an Alpha-based system (and viceversa). This capability sheds new light on how you can deploy and engagedifferent hardware platforms.

Beyond hardware compatibility, the ability of Octopus to mirror many kindsof data structures opens up a variety of backup and recovery options. You canuse Octopus to mirror a live SQL database and then create tape archives from thetarget system instead of the live, primary system. Octopus can mirror sharedfile areas that your end users access, and it can protect these areas from dataloss. You can mirror a Web system to reflect all production changes on a targetserver. Octopus even lets you mirror a server to a remote location (via awide-area link) as part of a disaster recovery plan. In short, Octopus can solvequite a variety of data protection problems.