Dell PowerVault MD3000 - Manual (Page 8)

8
Hardware Installation
Each RAID controller module has at least one SAS In port connector that
provides the direct connection to the host or node. A second SAS In port
connector is available on the optional dual-port RAID controller. SAS In port
connectors are labeled In-0 and, if using the optional controller, In-1(see the
PowerVault MD3000 Hardware Owner’s Manual for more information).
NOTE:
When you cable from a host server to an MD3000 SAS In port connector,
either Out port connector of the server’s HBA can be used.
Each MD3000 RAID controller module also contains a SAS Out port
connector. This port allows you the option to connect the RAID enclosure to
an expansion enclosure.
Cabling the Enclosure
You can cable your enclosure to up to four hosts and up to two expansion
enclosures. The configuration that you choose depends on the number of
hosts you have, whether you are connecting to a standalone host or a cluster
node, and the level of data redundancy that you need.
The figures that follow are grouped according to the number of SAS In port
connectors available on the MD3000. Single SAS In port configurations and
dual SAS In port configurations each support redundant and non-redundant
cabling.
Redundancy vs. Nonredundancy
Nonredundant configurations, configurations that provide only a single data
path from a host to the RAID enclosure, are recommended only for non-
critical data storage. Path failure from a failed or removed cable, a failed host
bus adapter, or a failed or removed RAID controller module results in loss of
host access to storage on the RAID enclosure.
Redundancy is established by installing separate data paths between the host
and the storage array, in which each path is to different RAID controller
modules. Redundancy protects the host from losing access to data in the
event of path failure, because both RAID controllers can access all the disks in
the storage array.