Connect The Back-End Cabling; Expansion Enclosure Cabling Guidelines; Back-End Sas Redundancy; Back-End Sas Port Types - Dell SC4020 Deployment Manual

Connect the Back-End Cabling

Back-end cabling refers to the connections between the storage system and expansion enclosures.
An SC4020 storage system can be deployed with or without expansion enclosures.
• When an SC4020 storage system is deployed without expansion enclosures, the storage controllers
must be interconnected using SAS cables. This connection enables SAS path redundancy between the
storage controllers and the internal disks.
• When an SC4020 storage system is deployed with expansion enclosures, the expansion enclosures
connect to the back-end SAS ports on the storage controllers.

Expansion Enclosure Cabling Guidelines

The connection between a storage system and expansion enclosures is referred to as a SAS chain. A SAS
chain is made up of two paths, which are referred to as the A side and B side. Each side of the SAS chain
starts at the initiator only SAS port on one storage controller and ends at the initiator/target SAS port the
other storage controller.
You can connect multiple SC200/SC220 expansion enclosures to an SC4020 by cabling the expansion
enclosures in series. You can also connect up to two SC280 expansion enclosures to an SC4020 by
cabling the expansion enclosures in series. However, the SC4020 does not support SC200/SC220
expansion enclosures and SC280 expansion enclosures on the same SAS chain.

Back-End SAS Redundancy

Use redundant SAS cabling to make sure that an unavailable I/O port or storage controller does not cause
a Storage Center outage.
If an I/O port or storage controller becomes unavailable, the Storage Center I/O continues on the
redundant path.

Back-End SAS Port Types

Each storage controller has two types of back-end SAS ports: initiator only and initiator/target.
The ports labeled A are initiator-only ports and the ports labeled B are initiator/target ports.
Figure 73. SC4020 Storage System SAS Ports
1. Storage system
Connect the Back-End Cabling
2. Storage controller 1
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