Disaster recovery (DR) plans are often based on the principle
of: “I will fail over instantaneously in the event of emergency,”
when frankly that’s not usually an option. How fast you can
fail over
is a vital part of the process of planning for DR, and cannot be
overlooked without consequence when an emergency hits. There are three main
points of time consumption to consider. First is the time-out before you take
action at all, next is the amount of time it takes to recover the data, and
finally the amount of time it takes to recover the system so users can get back
online.

Time to fail over generally will be decided by a combination
of technical and non-technical factors. The “time until declaration”
is the length of time it will take your technology staff to confirm that there
is an emergency in progress and that you must initiate DR procedures. This can
be a few seconds for local, automated failover systems, but could be hours for
remote or tape-restore solutions. Once you declare the disaster, you must also
factor in time for all of the steps required to get ready to fail over. This
could include travel to a DR site, recovery of tapes from an off-site storage
provider, etc.

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Data recovery may very well be the largest time factor to
consider if you have to restore from tape. Most drives can take up to several
hours to restore a server, and you can’t do much else until the data is back on
a spinning disk. You can minimize the hit by pre-configuring hardware to
immediately accept the restored data, but you still have to copy it from the
tape to the system. Replication tools are more expensive to put in place, but
save a tremendous amount of time by having the data already on disk when you
need to perform a failover process. Either way, you may need to mount volumes,
restore snapshots, or perform other tasks that can add significantly to your recovery
time.

Finally, once you’re ready to restore services, and the data
is back on the disks, you still have to take at least some time for last-minute
configuration and restoration of data systems. This can include reinstallation
of applications, re-routing of DNS systems to allow end-users to connect, and
other such tasks. Failover solutions can speed up this process, but you may
still need to tweak them, especially for more complex
solution sets and software packages
.

All told, instant failover is seldom a realistic option for DR
planning. There will always be some time spent during the process, but with the
right planning and tools you can minimize the delay. Find the combination of
features and functions that fits both your budget and your tolerance of
downtime, and you won’t be surprised if and when you find you have to fail over
quickly.