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Chapter 2: Hardware installation
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Fault-tolerant links to SAS disk drives
- The SAS expansion cables are bundled with the expansion systems. Take note that if there are
many expansion systems connected, a longer SAS external cable, approximately measured
120 cm, may be needed to connect an expansion system from the opposite direction for a
higher redundancy.
- One expansion link connects the expansion system from a storage system with HBA/RAID
card to the nearest expansion system, then to the most distant expansion system. Another
expansion link connects to the most distant expansion system, from the opposite direction to
the first expansion system from the storage system.
- Each expander controller on the SAS expansion system controls a
SAS domain
that connects
to one of the alternative interfaces of the disk drives in the enclosure. For example, one
expander unit controls Domain A while the other expander controls Domain B. In a fault-
tolerant topology, the SAS external links always connect to the SAS ports of the same SAS
domain.
- Identify the SAS domains by the location of the expanders: the left controller is controller A, the
right is controller B.
- On a storage system, each controller is considered as managing a separate SAS domain. With
the help of the port selector mechanism on the MUX boards, the idea of SAS domain applies
even when SATA drives are used in a dual-controller expansion system.
