IBM N Series Hardware Manual page 46

The IBM System Storage N series supports these expansion units:
EXN1000 SATA storage expansion unit
EXN2000 and EXN4000 FC storage expansion units
EXN3000 SAS/SATA expansion unit
EXN3500 SAS expansion unit
At least one storage expansion unit must be attached to the N series system.
All eight models must be mounted in a standard 19-inch rack. None of the eight include
storage in the base chassis
Dynamic removal and insertion of the controller
The N6000 controllers are hot pluggable. You do not have to turn off PSUs to remove a
controller in a dual-controller configuration.
PSUs are independent components. One PSU can run an entire system indefinitely. There is
no "two-minute rule" if you remove one PSU. PSUs have internal fans for self-cooling only.
RLM design and internal Ethernet switch on the controller
The Data ONTAP management interface, known as e0M, provides a robust and cost-effective
way to segregate management subnets from data subnets without incurring a port penalty.
On the N6000 series, the traditional RLM port on the rear of the chassis (now identified by a
wrench symbol) connects first to an internal Ethernet switch. This switch provides connectivity
to the RLM and e0M interfaces. Because the RLM and e0M each have unique TCP/IP
addresses, the switch can discretely route traffic to either interface. You do not need to use a
data port to connect to an external Ethernet switch. Set up of VLANs and VIFs is not required
and not supported because e0M allows customers to have dedicated management networks
without VLANs.
The e0M interface can be thought of as another way to remotely access and manage the
storage controller. It is similar to the serial console, RLM, and standard network interfaces.
Use the e0M interface for network-based storage controller administration, monitoring
activities, and ASUP reporting. The RLM is used when you require its higher level of support
features. Host-side application data should connect to the appliance on a separate subnet
from the management interfaces
RLM assisted cluster failover (CFO)
To decrease the time required for cluster failover to occur when there is an event, the RLM
can communicate with the partner node instance of Data ONTAP. This capability was
available in other N series models before the N6000 series. However, the internal Ethernet
switch makes the configuration much easier and facilitates quicker cluster failover, with some
failovers occurring within 15 seconds.
Reliability improvements
The N6000 series improves reliability as compared to its predecessors. Highlights include the
following improvements:
Fewer cables, eliminating external cables in cluster configurations
Embedded NVRAM eliminates the PCIe connector
There are fewer components, specifically, two fewer power supplies
Improved component de-rating guidelines result in less stress on components
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IBM System Storage N series Hardware Guide