IBM Systems Magazine, Mainframe - January/February 2018 - 9
disk drives, (virtual) tape, flash,
etc.), and how the integrity of
media is maintained. This view
focuses on maintaining a replica
of the current state of the storage
that can be quickly brought into
production use, minimizing the
disruption of business activities.
Solutions in this space are storage controller based (i.e., management of the recovery occurs based
on the configuration of the installation's storage controllers and connectivity network). These solutions
copy data as it's written from the
primary storage controllers to alternate storage controllers to ensure
that a reasonably up-to-date copy
is maintained (locally, at metro or
global distances). While a synchronous connection between the
primary and alternate copies is
required to minimize the recovery
time objective (RTO) and eliminate
data loss, asynchronous data
replication over longer distances
is more frequently used to ensure
better isolation between the primary and alternate copies, while
accepting a level of data loss within
the recovery point objective (RPO).
this view, a client can understand more about applications:
sequencing, what's running at a
point in time, data accessed by
each, and what data are in use at
a point in time.
An application may need to
access hundreds or thousands
of data sets that were generated
by other applications or previous
executions of that application,
and generate hundreds or thousands of new data sets, which
are used for other applications
or subsequent executions of the
The application view is critical
to recoverability in that it enhances
the storage and data views by providing contextual temporality of
data and execution dependencies.
At best, the storage view can maintain the integrity of "the now" (or
"the just before now") and the data
view can provide point-in-time
backups of individual data sets.
An application-centric solution
provides the ability to take
point-in-time backups at key
points in time and restore the
necessary data to restart with a
consistent set of data.
The data view examines the
ability to recover the logical
constructs that are maintained on
storage (e.g., volumes, data sets
and files). Solutions for recovering
the data view are based on system
software, storage controller firmware and hardware.
By understanding and managing the constructs within the
storage controllers, software
can make point-in-time copies.
However, recovering a complex
system requires more context
to understand how different
backups are related to the dependent applications.
The application view adds the
context of how the data is used
by the client's applications. From
Devise a Plan
For maximum resiliency, many
organizations rely on storage
replication as the primary approach
for DR and business continuity.
The data are divided into consistency groups (e.g., sets of related
data) typically by application.
The primary and alternate storage
controllers communicate changes
in the data while maintaining the
referential integrity within each
consistency group. The client and
vendor plan the placement of data
into consistency groups and configure the flow of changes to achieve
the necessary RTO and RPO.
The reason data replication
doesn't protect you from a
ransomware attack or application corruption is that a storage
controller replicates all data as
of related data
it's written. It can't distinguish
an "appropriate write" from an
"inappropriate write." This results
in alternate copies that are equally
corrupt as the production data.
To make an application or set of
applications recoverable requires
a backup copy ("snapshot") of all
application data that's consistent
at critical points in time and a
backup copy of the application
as it was running at those critical
points in time.
To protect snapshot copies from
corruption, they should be maintained on media that are isolated
from and secured differently from
primary production storage.
Understanding all of the
applications and data sets that
are critical to your environment is
a daunting task. Even small environments might have hundreds
of jobs accessing thousands of
related data sets. Large environments can have tens or hundreds
of thousands of jobs and millions
of data sets. Aside from the initial
complexity, the environment is
The size and complexity of the
problem demand a solution that
interrogates and understands
the application flow, data usage
and the relationship of that data
to all of the jobs within that
application. The solution should
perform backups at critical times
and maintain an inventory of the
backed up data.
When recovery becomes necessary, the solution should be able
to use that inventory to inform
administrators of the complete sets
of recoverable data, minimizing
the need for complex human analysis of the environment.
Finally, the solution must adapt
the recovery strategy to account
for changes in the environment.
With an application-centric solution, your organization can more
reliably recover your applications,
restoring service more quickly
after data corruption failures.
ibmsystemsmag.com JANUARY/FEBRUARY 2018 // 9