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Dell Unity systems have 2 on-board 12Gb SAS ports in each of the SPs in the Disk Processor Enclosure (DPE), for connecting to Disk Access Enclosures (DAEs). A 4-port 12Gb SAS I/O Module can also be provisioned in some Dell Unity systems in order to provide additional back-end buses. In general, the on-board SAS ports provide sufficient IOPS and bandwidth capabilities to support most workloads. The SAS I/O Module should be considered in systems which will require extremely high bandwidth performance (greater than 10GB/s), or will attach more DAEs or drives than are supported with the on-board buses, or will attach an 80-drive dense enclosure with high-bandwidth option. The SAS I/O Module occupies an I/O moduleslot that could otherwise be used for front-end connectivity.
When cabling DAEs to the DPE, balance them as evenly as possible across all available buses. When only the 2 SAS ports on each DPE are available, it is recommended to connect DAEs in the following order:
Connect additional DAEs in the same rotation.
When provisioning the 4-port SAS I/O Module, it is recommended to connect DAEs in the following order:
Once all buses have at least 1 connected DAE, connect additional DAEs in the same rotation.
80-drive dense enclosures can connect and intermix with other DAEs. When connecting multiple 80-drive enclosures to a system, place them on as many separate buses as possible, before daisy chaining them on a single bus.
80-drive dense enclosures can also be connected with a high bandwidth option that utilizes 2 SAS buses per enclosure, ganging them together for higher performance. This option is only available on Dell Unity systems that support the SAS I/O Module. Dell Technologies recommends connecting these enclosures with this high bandwidth option, when possible.
Flash drives have the highest performance potential of any drive type. Therefore, Dell Technologies recommends spreading Flash drives across all available buses while avoiding Flash drives and non-flash drives in the same enclosure, if possible, to ensure the best IOPS and service times.