Active-Active vs. Active-Passive - starline Computer GmbH

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INTRODUCTION
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ENTERPRISE CLASS STORAGE OS
for EVERY BUSINESS
The purpose of this document is to compare two high availability failover configurations, namely Active-Active and Active-
Passive, both being possible to configure using Open-E DSS V7 software*.
The comparison was entrusted with two tests conducted by the Open-E Quality Assurance Team, measuring respectively:
data throughput performance and failover switching time.
Apart from presenting tests results and conclusions, this document provides brief descriptions of both configurations.
.
*To take advantage of Active-Active functionality, an additional Feature Pack - Active-Active iSCSI Failover of the
Open-E DSS V7 software is required.
HIGH AVAILABILITY OVERVIEW
Last year (2011), Science magazine published an
interesting study presenting measurements of world’s
total technological capacity to communicate, store, and
compute information.
According to the publication: “in 2007, humankind was able
to store 2.9 × 10 20 optimally compressed bytes and carry
out 6.4 × 10 18 instructions per second on general-purpose
computers”[1]. At the same time: “general-purpose
computing capacity grew at an annual rate of 58%” [1].
With amount of data increment at this rate, the need to
effectively store data becomes a priority.
Thinking of “effective” ways of storing data – the key
element is continuous availability of storage solutions.
Availability of resources is one of the concerns of Business
Continuity. Planning involved in that field is about ensuring
that companies will be able to operate in case of a serious
disruption.
IT components availability has become increasingly
important since businesses are more and more dependent
on digital information and technology.Considering
industries as candidates for implementing high availability
solutions, we can name healthcare, banking, online
retail and many more. All of them require continuous,
uninterrupted access to their resources.
A standard for availability of the products or systems is
known as “class of 9s”.
Downtime Costs $26.5 Billion in Lost Revenue
It refers to the percentage figures used for the
representation of high availability (e.g. 99.999% is five
nines). For example, in case of availability value of 98 %,
the downtime will equal 2 %. Downtime easily translates
to lost revenue.
High availability is a goal for storage solutions. The priority
is for data or services to be accessed at all times, even if
malfunction occurs. This can be achieved in a number of
ways involving clustering, redundancy and software that
handles the failover configurations.
High Availability clusters, with priority to decrease
downtime to a minimum, are one of the implementations
of these solutions. Such clusters are usually supported by
storage management software and Open-E DSS V7 can be
an example of those.
Typically, a high availability cluster consists of two nodes.
In case of a node failure, the client network connections
and file systems are moved or mounted to the other node,
so the downtime is minimized or eliminated completely.
An operation of switching to a redundant or synchronized
node is called failover. In contrast, failback is the process
of restoring a system, component or service to a state
before failure.
There are two major configurations for implementation
of high availability storage solutions – Active-Passive
and Active-Active. Let us briefly describe them, before
presenting the results.
“…more than $26.5 billion in revenue is lost each year from IT downtime, which translates to roughly $150,000 is lost
annually for each business (…). Of the 200 companies surveyed, small enterprises lost, on average, more than $55,000
in revenue due to IT failures each year, while midsize companies lost more than $91,000 and large companies lost
more than $1,000,000.”
Source: Information Week, 2011 [2].