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Dell Unity™ All Flash and Unity Hybrid Hardware Information Guide

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Cabling the DPE to a DAE

If you have one or more DAEs, these components must be cabled to the DPE back-end ports so that the storage is available in the system. Typically, the DAE(s) that are to be directly connected to the DPE need to be located close enough to the DPE so that the 2-meter DPE-to-DAE interconnect cables can be routed and connected to the DPE easily. 5- and 10-meter interconnect cables are available when you need to connect enclosures across multiple racks.

NOTE:General DAE back-end bus configuration rules:
  1. Maximum number of enclosures per bus is 10.
  2. Maximum number of drive slots per bus is 250, up to specific system limitations for drive slots.
  3. For best performance, evenly distributing DAEs across the available back-end buses is recommended.
Consider the maximum number of drives supported by the storage system model. DAEs can be added to the system while the operating system is active and up to the DAE and drive slot limit for the storage system. DAEs or drive slots over the system limit will not be allowed to operate with the system.

Shown in the upcoming figures are examples of two-bus SAS cabling in this DPE-based storage platform. The storage processors connect to the DAEs with mini-SAS HD cables. The cables connect LCCs in the DAEs of a storage platform in a daisy-chain topology.

The mini-SAS HD ports on the storage processors in the DPE are labeled 0 and 1. Mini-SAS HD port 0 is connected internally to the SAS expander that connects the drives on the front of the DPE. The DPE and its front facing drives begin the first back-end bus, BE0, and is automatically enclosure 0 (EA0). We refer to the address of this enclosure as BE0 EA0.

NOTE:Each DAE supports two completely redundant connections to the DPE (LCC A and LCC B).

Since mini-SAS HD port 0 is already connected internally to the DPE drives, it is recommended that you connect the first optional DAE to the mini-SAS HD output port 1 of each storage processor to begin back-end bus 1 (BE1) and designate this DAE as enclosure 0 of this bus. We refer to the address of this enclosure as BE1 EA0.

In a two back-end bus system, it is recommended that you connect the second optional DAE to the mini-SAS HD port 0 of each storage processor.

DAE load balancing

If your system has several optional DAEs, you can daisy-chain them within that bus. However, it is recommended that you balance each bus. In other words, always optimize your environment by using every available bus, and spreading the number of enclosures and drives as evenly as possible across the buses.

The rule of load or bus balancing is applied to all DAEs. BE0 EA0 (0_0) is the DPE (SP A and B). So, to balance the load, the first DAE (LCC A and B) in the cabinet is BE1 EA0 (1_0) and with the second DAE BE0 EA1 (0_1), and so on.

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