EMC CX500I Configuration Guide - Page 96

Multiple Paths to LUNs, Disk IDs, Sample Shared Switched Installation, Fibre Channel switches.

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Planning File Systems and LUNs Multiple Paths to LUNs A shared storage-system installation includes two or more servers and one or more storage systems, each with two SPs and the Access Logix option. Often shared storage installations include two or more Fibre Channel switches. Shared storage (switched or direct) provides at least two paths to each LUN in the storage system. The Access Logix software detects all paths and, using optional PowerPath® failover software, can automatically switch to the other path, without disrupting applications, if a device (such as a host bus adapter or cable) fails. And with two adapters and two SPs, PowerPath can send I/O to each available path in a user-selectable sequence (multipath I/O) for load sharing and greater throughput. Unshared storage, if the server has two adapters, provides two paths to each LUN. With two adapters, PowerPath performs the same function as with shared systems: automatically switches to the other path if a device (such as host bus adapter or cable) fails. Disk IDs Disk IDs have the form b e d, where b is the back-end loop (also referred to as a back-end bus) number (0, or 1) e is the enclosure number, set on the enclosure rear panel (0 for a DPE2 and the first DAE2 with an SPE) d is the disk position in the enclosure (left is 0, right is 14) Sample Shared Switched Installation Figure 5-1 and the table that follows it show a sample shared storage system connected to three servers: two servers in a cluster and one server running a database management program. Note that Figure 5-1 shows a single-cabinet storage system. You can configure a storage system with two cabinets so that all the disks in 5-2 EMC CLARiiON CX300, CX500, CX500i, and CX700 Storage Systems Configuration Planning Guide

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5-2
EMC CLARiiON CX300, CX500, CX500i, and CX700 Storage Systems Configuration Planning Guide
Planning File Systems and LUNs
Multiple Paths to LUNs
A shared storage-system installation includes two or more servers
and one or more storage systems, each with two SPs and the Access
Logix option. Often shared storage installations include two or more
Fibre Channel switches.
Shared storage (switched or direct) provides at least two paths to
each LUN in the storage system. The Access Logix software detects
all paths and, using optional PowerPath
®
failover software, can
automatically switch to the other path, without disrupting
applications, if a device (such as a host bus adapter or cable) fails.
And with two adapters and two SPs, PowerPath can send I/O to each
available path in a user-selectable sequence (multipath I/O) for load
sharing and greater throughput.
Unshared storage, if the server has two adapters, provides two paths
to each LUN. With two adapters, PowerPath performs the same
function as with shared systems: automatically switches to the other
path if a device (such as host bus adapter or cable) fails.
Disk IDs
Disk IDs have the form
b e d
, where
Sample Shared Switched Installation
Figure 5-1 and the table that follows it show a sample shared storage
system connected to three servers: two servers in a cluster and one
server running a database management program.
Note that Figure 5-1 shows a single-cabinet storage system. You can
configure a storage system with two cabinets so that all the disks in
b
is the back-end loop (also referred to as a back-end bus)
number (0, or 1)
e
is the enclosure number, set on the enclosure rear panel (0 for
a DPE2 and the first DAE2 with an SPE)
d
is the disk position in the enclosure (left is 0, right is 14)