With storage
needs spiraling upward, it's simply impractical to keep every piece
of corporate data on expensive, high-performance
Fibre Channel discs.
The practice of
tiered storage has emerged as a way to mitigate this expense by
keeping mission-critical data on the fastest disc platforms while
relegating less valuable data to slower and less expensive storage,
such as
SATA disc or even tape. In most cases, an organisation will
establish and maintain several different storage tiers. But,
organising corporate data into tiers is hardly straightforward.
First, data must be classified to understand the relative value
of each file or file type. Data types that are only infrequently
accessed, such as email, are often indexed and stored with
automated archiving tools. Data then has to be migrated between
storage platforms so that it can be stored according to its
classification. This Buying Guide covers the major product
considerations involved in tiered storage initiatives. Each chapter
offers a set of buying points and product specifications that can
help readers identify prospective new tiered storage products.
Before we look at specific product categories, let's start by
identifying the core concerns when considering tiered storage.
Establish data retention policies in advance. Most
organisations are obligated to retain certain data types in order
to meet compliance and litigation needs and then delete that data
after its retention period expires. However, retention policies are
not set automatically -- no software can tell you how long you
should keep a piece of data. Instead, retention is defined by
understanding the value of each data type and its relationship to
compliance. Data migration and archiving tools can then be used to
enforce the established retention policies across your storage
tiers.
Have a data categorisation plan formulated in advance.
Data classification is not automatic -- no software can determine
the actual value of data to your own organisation, so don't rely on
data classification tools to make classification decisions for you.
Data classification is a human process that involves understanding
and input from many departments, like human resources, finance and
legal. Once you have established the relative value of each data
type, data classification tools can then find the data, apply
metadata and enforce established retention policies. Experts note
that the most successful tiered storage deployments occur when
categorisation and retention policies are already mature and
proven.
Consider the management impact of additional storage
systems. Tiered storage often involves the use of multiple
storage systems, and this can sometimes present more of a burden
for storage administrators. For example, Tier 1 storage may reside
on a Fibre Channel
storage area network (San), Tier 2 storage may reside on a SATA
network attached storage (Nas) and Tier 3 storage may exist on a
content-addressed storage (CAS) archiving system, virtual tape
library (VTL) or tape library. For some organisations, the added
cost and management overhead imposed by multiple storage tiers can
overcome the benefits, and experts note that some large data
centers are actually abandoning their tiered storage in favor of a
single tier.
Set realistic savings expectations. While the ultimate
objective of tiered storage is to save money, the actual savings
often falls below expectations. For example, experts note that Tier
2 storage should cost 20% to 30% less than Tier 1, while Tier 3
storage should cost 50% to 60% less. In actual practice, however,
experts only see a savings of 10% to15% at Tier 2 and only 30% to
40% savings at Tier 3. Below expectation savings is another reason
why some enterprises revert to a single storage tier.
Buy the
tool that best fits your needs. You will find a multitude of
migration, archiving and data classification tools to help automate
your own tiered storage environment. But, there can be a tremendous
difference in the complexity, cost and capability of those tools.
There are many possible examples. Some products may offer a
relatively simple and focused tool, like Brocade Communications
Systems Inc.'s Data Migration manager, while other products may
provide a sophisticated suite of functions, like Enterprise Vault.
Similarly, you may select a tool that is intended for a specific
storage platform, such as EMC Corp.'s SRDF or opt for a more
heterogeneous tool, such as Incipient Inc.'s Network Storage
Platform (NSP). Finally, some tools may address specific
applications, such as Mimosa Systems Inc.'s NearPoint for Microsoft
Exchange Server, while other tools may support a wide range of
applications. Experts suggest that you focus on meeting your
minimum performance criteria, rather than being distracted by
potentially unnecessary value-added features.
Consider the
potential for performance improvements. When all storage is
located on a single tier, the contention for user and application
access can adversely influence storage system performance. That
contention can ease by spreading out access across multiple storage
tiers. Even though SAS or SATA drives may offer lower performance
than Fibre Channel drives, reduced competition for access may
actually allow for good performance at the SAS or SATA tier. And,
since this also reduces the number of requests arriving at Fibre
Channel drives, the top tier performance may also improve.
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