Avago Technologies Syncro 9361-8i - Manual (Page 5)

Avago Technologies
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Syncro CS 9361-8i and Syncro CS 9380-8e Solution User Guide 
October 2014
Chapter 1: Introduction
Concepts of High-Availability DAS
Chapter 1: Introduction
This document explains how to set up high-availability direct-attached storage (HA-DAS) clustering on a Syncro CS
9361-8i and Syncro CS 9380-8e configuration after you configure the hardware and install the operating system.
The Syncro CS solution provides fault tolerance capabilities as a key part of a high-availability data storage system. The
Syncro CS solution combines redundant servers, Avago HA-DAS RAID controllers, computer nodes, cable connections,
common SAS JBOD enclosures, and dual-ported SAS storage devices.
The redundant components and software technologies provide a high-availability system with ongoing service that is
not interrupted by the following events:
 The failure of a single internal node does not interrupt service because the solution has multiple nodes with
cluster failover.
 An expander failure does not interrupt service because the dual expanders in every enclosure provide redundant
data paths.
 A drive failure does not interrupt service because RAID fault tolerance is part of the configuration.
 A system storage expansion or maintenance activity can be completed without requiring an interruption of
service because of redundant components, management software, and maintenance procedures.
1.1 Concepts of High-Availability DAS
In terms of data storage and processing, High Availability (HA) means a computer system design that ensures a high
level of operational continuity and data access reliability over a long period of time. High-availability systems are
critical to the success and business needs of small and medium-sized business (SMB) customers, such as retail outlets
and health care offices, who cannot afford to have their computer systems go down. An HA-DAS solution enables
customers to maintain continuous access to and use of their computer system. Shared direct-attached drives are
accessible to multiple servers, thereby maintaining ease of use and reducing storage costs.
A cluster is a group of computers working together to run a common set of applications and to present a single logical
system to the client and application. Failover clustering provides redundancy to the cluster group to maximize up-time
by utilizing fault-tolerant components. In the example of two servers with shared storage that comprise a failover
cluster, when a server fails, the failover cluster automatically moves control of the shared resources to the surviving
server with no interruption of processing. This configuration allows seamless failover capabilities in the event of
planned failover (maintenance mode) for maintenance or upgrade, or in the event of a failure of the CPU, memory, or
other server failures.
The Syncro CS solution is specifically designed to provide HA-DAS capabilities for a class of server chassis that include
two server motherboards in one chassis. This chassis architecture is often called a cluster in a box (CiB).
Because multiple initiators exist in a clustered pair of servers (nodes) with a common shared storage domain, there is a
concept of device reservations in which physical drives, drive groups, and virtual drives (VDs) are managed by a
selected single initiator. For HA-DAS, I/O transactions and RAID management operations are normally processed by a
single Syncro CS 9361-8i controller or Syncro CS 9380-8e controller, and the associated physical drives, drive groups,
and VDs are only visible to that controller. To assure continued operation, all other physical drives, drive groups, and
VDs are also visible to, though not normally controlled by, the Syncro CS controller. This key functionality allows the
Syncro CS 9361-8i and Syncro CS 9380-8e solution to share VDs among multiple initiators as well as exclusively
constrain VD access to a particular initiator without the need for SAS zoning.
Node downtime in an HA system can be either planned and unplanned. Planned node downtime is the result of
management-initiated events, such as upgrades and maintenance. Unplanned node downtime results from events
that are not within the direct control of IT administrators, such as failed software, drivers, or hardware. The Syncro CS
9361-8i and Syncro CS 9380-8e solution protects your data and maintains system up-time from both planned and
unplanned node downtime. Also, it enables you to schedule node downtime to update hardware or firmware, and so