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There are six SAS connectors on the rear of the EXP24S drawer to which two SAS adapters
or controllers are attached. They are labeled T1, T2, and T3. There are two T1, two T2, and
two T3 connectors. While configuring the drawer, special configuration feature codes indicate
for the plant the mode of operation in which the disks and ports are split:
In mode 1, two or four of the six ports are used. Two T2 ports are used for a single SAS
adapter, and two T2 and two T3 ports are used with a paired set of two adapters or dual
adapters configuration.
In mode 2 or mode 4, four ports are used, two T2 and two T3 to access all SAS bays.
Figure 2-26 shows the rear connectors of the EXP24S drawer, how they relate to the modes
of operation, and disk grouping.
Figure 2-26 Rear view of EXP24S with the 3 modes of operation and the disks assigned to each port
An EXP24S drawer in mode 4 can be attached to two or four SAS controllers and provide
high configuration flexibility. An EXP24S in mode 2 has similar flexibility. Up to 24 HDDs can
be supported by any of the supported SAS adapters or controllers.
The most common configurations for EXP24S with Power Systems are detailed in 2.12.2,
"EXP24S common usage scenarios" on page 74. Not all possible scenarios are included. For
more information about SAS cabling and cabling configurations, search for "Planning for
serial-attached SCSI cables" in the IBM Knowledge Center, which can be accessed at:
http://www.ibm.com/support/knowledgecenter/POWER8/p8hdx/POWER8welcome.htm
Chapter 2. Architecture and technical overview
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