Disaster Recovery
Software
Disaster recovery
software can have pitfalls if you are not committed to the project
and what you get out of it. You know, what comes out is only as good
as what goes in etc! Is there a difference between Business
Continuity software and Disaster Recovery Software? In some ways,
yes and in other ways, no.
Disaster Recovery
Software - OPTIONS
Typically disaster
recovery software refers to the more technical software to enable
your plan that you have perhaps used some form of Business
Continuity software to come up with. There are generally two main
types, defined by the methodology used to replicate data from one
location to another: synchronous and asynchronous data transfer
systems.
Both DR systems let
you create up-to-the-second backup copies of your valuable
production data in another physical location. This feature allows
the data to survive intact if the data center is lost for some
reason, just as in a terrorist act or fire. Unlike tape backup
systems, the data is current and in a useable format, as it is
already on a disk system and not stored on a tape, which must be
restored to disk.
Disaster Recovery
Software - Synchronous
Synchronous systems
are designed to make sure that no I/O transaction can be committed
to the disk of the primary system unless and until it has also been
committed to the disk systems of the backup system.
Most of these systems
are hardware based and involve the use of attached storage, like NAS
or SAN systems. However, software-based synchronous systems are also
available today.
Disaster Recovery
Software – Asynchronous
For most applications
and businesses, asynchronous DR technologies offer a much more
cost-effective, but still quite
sufficient—solution.
These systems are
generally software-based and reside on the host server rather than
on the attached storage array. They can protect both local and
attached disk systems. In an asynchronous system, I/O requests are
committed to the primary disk systems immediately while a copy of
that I/O is sent via some medium (usually TCP/IP) to the backup disk
systems.
Since there is no
waiting for the commit signal from the remote systems, these systems
can send a continuous stream of I/O data to the backup systems
without slowing down I/O response time on the primary
system.
Most asynchronous
systems have some methodology to make sure that if something is lost
in transmission, it can be re-sent.
The main drawback is
the potential for a few transactions to be lost during a failover
event. If the primary server suddenly goes offline, anything waiting
to be transmitted to the backup system will be lost. However, since
this usually involves only a few transactions, the performance of
asynchronous systems is well within the required parameters of
almost all business applications.
