Realtime data mirroring over network connections
Maintaining duplicates of up-to-date
information is a key capability for a fault-tolerant (or fault-resilient)
environment. One way to implement this capability is to designate a system as a
hot backup to one or more primary systems and to mirror information from the
primary system to the target system. If a primary system fails, the target
system can replace it without losing data because an exact copy of the primary
system's crucial information is on the backup.
Mirroring is a powerful and sophisticated capability that you don't expect
to find on a couple of diskettes in a shrink-wrapped box. And that capability is
what makes Octopus such an interesting, and in many ways, unique product.
Octopus is a realtime data mirroring software product that Octopus
Technologies developed and markets. The product runs on all NT platforms (Intel,
MIPS, Alpha, and PowerPC), operates under both NT Server and Workstation (and
Windows 95), with any type of network connection--even wide-area RAS links--to
carry the mirrored information from one system to another. Octopus can mirror
data from one system to another, from several systems to one system, or from one
system to several. Two systems can even mirror and thus back up each other. All
these features make Octopus a flexible product for a variety of mirroring
strategies.
Speed is the feature that makes Octopus impressive. It tracks updates as
they occur and then mirrors just the updated information across the network. The
result is blazingly fast data delivery; the software delivers updated data to a
target 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 expect
Octopus to perform well in any LAN environment.
Another benefit is that this product lets you mirror information structures
ranging from simple flat files to sophisticated databases such as Microsoft's
SQL Server. In fact, the only type of file access that Octopus Technologies
admits to not being able to handle is the update access that the Microsoft Write
accessory program uses. Fortunately, Write is a minor application that doesn't
often 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 a
Micron configured with NT Server 3.51 and a Toshiba laptop running NT
Workstation 4.0 beta 2. A garden-variety 10Mbit-per-second Ethernet network
interconnected all the systems; I used no switching hubs or other
speed-enhancing devices.
Installing Octopus is easy, but you have to reboot to activate it. You must
install Octopus on both the primary (source) system and backup (target) system
before you can configure and use it. With other products, you need to configure
only the primary system; the target system receives the configuration
information from the primary system.
At a minimum, you must identify the primary system's files and directories
that you want to mirror to the target. The product's term for these file and
directory specifications is data vaults. Screen 1 shows the dialog for
entering this information. When you add the information about the target system,
you can have Octopus query the network to sniff out all the systems running
Octopus software, or you can enter the target system's name. If you have a
medium or large LAN, having Octopus query the network can be time consuming, so
enter the target system name manually; Octopus will validate the connection
after you enter the name.
You can configure multiple specifications to enable one-to-many mirroring
or to mirror multiple file sets to one target system. All the data vaults you
define appear in the lower half of the configuration dialog. You can modify or
delete those specifications. You can also select the network protocol (TCP/IP,
NetBEUI, or Internet Packet eXchange--IPX) for transporting mirrored
information. 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 verify
that the files on the primary and target system are identical and copy files
that need refreshing.