Migrating from legacy storage with the minimum disruption
requires a good strategy, support from the business and the right
technology, such asstorage virtualisationor the use of migration
appliances.
Before carrying out any migration, it is wise to analyse the
content of the data. Web documents, web pages and e-mails can
constitute 80% of a company's data, with 50-60% of the documents
stored being duplicates, says Nic Archer, senior vice-president of
enterprise migration specialist Vamosa.
"By analysing your content - its current state and its quality -
in advance, you can reduce the challenge of migration," he says.
Data de-duplication can also bring significant cost
savings.
As well as analysing the content, organisations can
ease migration by carefully examining how applications are
accessing the storage (for example files, databases and raw
volumes), and by looking at the connectivity that is being used
(direct attached, fibre channel SAN, or IP SAN).
"As well as the data movement itself, the other consideration in
any migration project is the need to change the host device drivers
and/or path management drivers to suit the new storage devices.
This may in turn have dependencies on operating system levels,"
advises Steve Legg, CTO at IBM System Storage.
Migration events
The secret to minimising disruption when
migrating storage is to build the plan around migration events
related to the storage that is linked to particular servers and
applications, says storage specialist Tony Reid, UK services
director at Hitachi Data Systems.
"A good plan will give a single application outage, keeping the
rest online," he says.
Organisations looking to perform data migration face a Catch-22
situation, says Roger Llewellyn, chief executive officer of
Kognitio, which has migrated data for the likes of Prudential and
Bupa.
He explains that a "big bang" migration, where all data is
migrated in a single action, requires rigorous testing and
auditing, which can mean lengthy downtime of 10 days or more.
The alternative, migrating data piecemeal over a longer period,
means that as systems are constantly changing and growing, the
migration will need to continually adapt to these changes, taking
longer and longer. "Either way, while a migration might be
effective, the problems involved will become crippling," says
Llewellyn.
One of the ways to reduce the testing time in big bang
migrations is to use analysis and testing tools which use in-memory
and massively parallel data processing techniques so tests can be
conducted quickly, and migrations shortened to less than 48 hours
in some cases.
Storage virtualisation
Many industry experts argue that
virtualisation brings the capability to migrate efficiently
from legacy storage.
Sean Haffey, storage business manager at Fujitsu Technology
Solutions, says that with virtualisation, migration to new
technology, whether a new tape robot or disc, is handled quickly
and transparently. "Payback is typically 12 to 15 months, which for
a large project such as this is an exceptional schedule for
ROI."
Nick Broadbent, European director at DataCore, which frequently
carries out legacy data migrations, says problems are often caused
by different manufacturers' storage subsystems not communicating
well with each other.
However, storage virtualisation brings a new flexible world,
says Broadbent. "Moving data from unlike storage, from legacy to
new, can be done in place without disruption."
Appliance-based storage migration products such as IBM's SVC,
DataCore and FalconStor, and application-level tools such as
Softek's TDMF, have been available for a number of years, and many
use storage virtualisation technology to move data and applications
between storage arrays.
But there is a new breed of appliance-based products, which
includes Incipient, HP's SVSP (based on LSI's SVM), HDS's USP and
NetApps' Filer Gateway, says Mark Sweeney, technical architect at
Logicalis UK.
"These allow a seamless migration between the older legacy
arrays and the newer, current arrays, and also enable such
migrations to occur without interruption to the business," he
adds.
But Sweeney says it is important not to be dazzled by some of
these new technologies, which can add cost and complexity and may
still be in the early adopter stage.
"While it won't be the case forever, the use of tapes is still a
popular and effective migration technique, offering a lower-risk,
non-destructive and cheaper migration," he says.