EMC Symmetrix DMX-3, Руководство по эксплуатации продукта

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164 EMC Symmetrix DMX-3 Product Guide
Data Integrity, Availability, and Protection
PowerPath then fails over the existing I/O request to another active
path to maintain data access and application availability—offering
intelligent load-balancing capabilities to optimize performance and
minimize bottlenecks. All this occurs transparently to the host so the
application is not stopped and data is continuously available. Once
the failed path is fixed or repaired, PowerPath automatically detects
activity, brings the path back into operation, and automatically sends
I/O requests down to the now-active path. The major benefits of the
path failover capability is the ability to automatically detect a channel
failure, transparently redirect an I/O to other available channels, and
easily service and restore the failed channel without interrupting
applications.
Internal control data
path redundancy Each director has two paths to connect the Symmetrix DMX message
matrix between each director. Independent and redundant fault
domains are provided by a plug-in Communications and
Environmental Control Module (XCM). These fault domains within
the message matrix fabric are intelligent at the hardware level and
load balance traffic between each domain. In the event that a fault
occurs within one of the domains, the traffic is automatically routed
by the hardware to the available domain, and the system is alerted of
the faulty XCM domain for replacement. The connection is made
through the plug-in XCM.
There are two XCMs per system. If we look at a fully configured
Symmetrix DMX, for example, 16 directors are configured with 32
point-to-point serial connections. This means 16 connections are
routed to the first XCM and the other 16 redundant connections are
routed to the second XCM. The message engine (ME) component of
the message matrix provides protection against rogue or runaway
nodes. This is done at each message engine through error correction
coding configurations, allowing the nodes to receive messages.
Packet CRC and sequence numbers protect each message packet
transmitted. Internal data paths with the message engine and fabric
element are fully parity protected.
Fibre Channel
back-end
redundancy The Symmetrix DMX architecture incorporates a 2 Gb/s Fibre
Channel back-end design to ensure high performance and full
redundancy. The Fibre Channel back-end disk subsystem provides
redundant paths to the data stored on the disk drives to provide
nonstop access to information, even in the event of a component
failure or replacement.