54
Designation
Description
Designation
Description
1
Controller A
5
Dual-ported SAS drives
2
Controller B
6
Expander
3
Expansion enclosure
controller A
7
To another expansion
enclosure
4
Expansion enclosure
controller B
-
Fault-tolerant Links to SAS disk Drives
-
SAS expansion cables will be available with the expansion enclosures. Note that if many expansion
enclosures are connected, a longer SAS external cable (e.g., a 120cm cable) may be necessary for
connecting a expansion enclosure from the opposite direction offering high redundancy.
-
One expansion link connects expansion enclosures from Unified Storage System to the nearest
expansion enclosure, and then to the farthest expansion enclosure. Another expansion link connects to
the farthest expansion enclosure from the opposite direction and then to the nearest expansion
enclosure.
-
Each expander controller on the SAS expansion enclosure controls a “
SAS Domain
” that connects one
of the alternative interfaces on all of the disk drives in the enclosure. For example, one expander unit
controls Domain A, and the other controls Domain B. In a fault-tolerant topology, the SAS external links
always connect to the SAS ports on the same SAS Domain.
-
The SAS Domains can be identified by the expanders’ locations, i.e., upper controller slot (Controller
A/Slot A) or the lower controller slot (Controller B/Slot B).
-
On the Unified Storage System, each controller can be 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 enclosure.
