IBM System Storage DS3300, Installation, User'S, And Maintenance Manual

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Redundant drive channel pair
Each RAID controller on the DS3300 has a drive expansion channel that contains
an x4 SAS port. The storage expansion enclosures that are connected to this
connector form a drive channel. The maximum number of hard disk drives that can
be installed in one drive channel is 48. In a dual-controller DS3300, one drive
channel from each controller combines to form a redundant drive-channel pair.
Figure 15 shows an example of a redundant drive-channel pair. If any component of
the drive channel fails, the RAID controllers can still access the storage expansion
enclosures in the redundant drive-channel pair.
Note: To support dual redundant drive paths, you must install the optional second
ESM in storage expansion enclosures that are connected to a dual-controller
storage subsystem.
DS3300
RAID controller A RAID controller B
SAS cable
SAS cable
EXP3000
To DS3300 RAID
controller A
To DS3300 RAID controller B
SAS cable
SAS cable
EXP3000
SAS cable
SAS cable
EXP3000
Figure 15. Example of a redundant drive path
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System Storage DS3300 Storage Subsystem: Installation, User’s, and Maintenance Guide