Storage Area Networks For Dummies®

Chapter 13: Using Data De-Duplication to Lighten the Load
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Some solutions that work at the client may still need to send duplicate files to
a central appliance before the duplicate files are eliminated; others are more
intelligent and communicate with the client to ensure that the only objects
sent are those that don’t already exist at the central site. Make sure that your
solution is in the latter category; otherwise, you may end up spending more
than necessary on WAN bandwidth for remote client backup.
Data replication
One of the highest expenses for data replication is the WAN bandwidth needed
to move all data changes to a DR site. (You can find more information on DR
in Chapter 6.) The more data you have to replicate, the more bandwidth you
need to move it. Many companies try to reduce their costs by replicating only
specific mission-critical datasets or by using lower-bandwidth links and living
with the amount of time it takes to get the data to the other side.
When companies need to move massive amounts of data for disaster recovery,
it makes a lot of sense to de-duplicate the data so it can be replicated more
efficiently using a less costly network. Delta versioning solutions work great
for reducing the amount of data that has to be moved and still enable you to
recover your applications very rapidly for DR.
Data retention
Long-term archiving is another wonderful opportunity to lower storage costs
by storing only one instance of everything in the archive. Suppose that you
need to keep data around for 5 weeks (as shown in Figure 13-12, earlier in this
chapter). Would you rather have to buy 101TB worth of tapes or just a bit
over 24TB to store the same amount of data?
VTL solutions with de-duplication provide a great way to store your data on
disk in de-duplicated format for long periods. If you need to conform to regulatory
requirements and store your data in immutable format, make sure that
your solution also can store data in WORM (Write Once Read Many) format.
WORM tape is a good solution for compliance; it takes no power, can hold a
great deal of data, is removable, and is fairly inexpensive.
Applications for which data de-duplication
doesn’t make sense
Frequently accessed production databases are the worst place to use data deduplication.
Imagine trying to keep performance up while each write operation
to the database disks must be preceded by a hash process to store the new