IBM N Series, Implementation Manual

Page: 25 / 105

Chapter 1: Implementation Overview 11
Understanding storage provided by native disk shelves
Connections and
loops Disks are inserted in disk shelves connected to the gateway or N series storage
controller. The connection from a storage controller to the disk shelves, which
might be daisy-chained, is sometimes called a
loop . The loops are described as
follows:
◆
The A loop or A channel is the connection from the storage controller to the
A port on the disk shelf module (not the A port on the storage controller or
host bus adapter).
◆
The B loop or B channel is the connection from the storage controller to the
B port on the disk shelf module (not the B port on the storage controller or
host bus adapter).
On a stand-alone system, you can use one or two connections between the
storage controller and the disk shelf. Using two connections provides
redundancy. A connection can be from any free FC initiator port on the storage
controller; if you are using just one connection, that connection can be to either
disk shelf module.
In an HA pair, you have the option to provide redundant connections through the
Data ONTAP Multipath Storage feature. (See Appendix B, “
Setting up and
Managing Multipath Storage ,” on page 65 for more details.)
The following illustration shows a stand-alone system with two redundant
connections to the disk shelf, one to each disk module.
A
B
O u t In
In O u t
G a tew a y
s tor a ge controller
Connection s to
third-p a rty s tor a ge a rr a y s
Di s k s helf 1
B loop A loop
0 a 0 b 0c 0d