Tape versus disk.
The debate over deploying tape or disk for data storage has existed since
the inception of these media types. As rich media and other data swell
to immense proportions for enterprises and governments, the storage media
controversy seems to intensify. However, the selection is not that simple.
In fact, there is no one choice. Instead, for most large data stores,
a media blend (i.e., disk, tape, etc.) rather than a single media type
better satisfies customer prerequisites for cost-effective and efficient
data storage and access.
In the November and
December 2001 issues of this publication, Diamond Lauffin of Nexsan Technologies
authored a series of well-constructed and informative articles titled,
"The Arrival of Affordable Disk-To-Disk (D2D) Storage." Mr.
Lauffin's thesis maintained that the use of tape media for primary backup
makes less sense today because of the lower total cost of ownership of
newer, faster disk arrays. He is correct. Technological advances and manufacturing
efficiencies have made disk media better than ever, giving both consumers
and enterprises more "bang for the buck." And for primary backup
that aids business continuation in case of a disaster or other type of
problem, disk makes sense.
But the author's enthusiastic
approach to disk seems to have lessened the value of current tape technology
and the software that manages it. Mr. Lauffin writes, "Maintaining
tape can involve such tasks as identifying and retrieving tape volumes,
monitoring tape bar code sequences, loading and unloading tape, inspecting
tape for wear, rotating tape, manual disaster recovery operations, and
inventory management." Had this been written five years ago, the
author would have been accurate. But looking at tape storage today as
simply an off-line, archaic archive technology can be deceptive. In fact
"it's interesting to note that despite some predictions to the contrary,
tape storage remains typically the ultimate resting spot for data."(1)
In addition, missing
from Mr. Lauffin's series is that tape, in the form of "near-line"
database extensions for infrequently used or "dormant data"
is still very much an applicable technology, on par with and more cost-effective
than disk (when used with disk arrays in a tiered storage system). So
let's take a look at where tape does fit in the storage hierarchy, and
where advances in tape technology and the software that manages it, make
tape as relevant and as cost-effective as ever.
According to Bill
Inmon, noted data warehousing consultant and Partner of BillInmon.com,
"…as data warehouses pass the three to four terabyte range they
need to be split over multiple hierarchies of storage media."(2)
The reason Inmon gives is that data should be divided between "active"
and "inactive." Active data is frequently accessed, business-critical
information needed for operational functions. Inactive data, though also
vitally important, is seldom accessed and tends to be more of historical
value for analytical tasks and customer relationship management (CRM)
applications. Inmon states, "Keeping huge amounts of dormant [inactive]
data on disk storage is like clogging the arteries with cholesterol. By
moving unused data off of high performance disk storage, the system is
scrubbed and only actively used data remains. In doing so, performance
really zips."(3)
