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GLYPH<SM590000> Each RPC card has two firmware images. If an RPC firmware update fails, the RPC card can still boot from the other firmware image. This design also leads to a reduced period during which one of the RPC cards is unavailable because of an RPC firmware update. Because of the dual firmware image, an RPC card is only unavailable for the time that is required (only a few seconds) to boot from the new firmware image after it is downloaded. Because of this configuration, full RPC redundancy is available during most of the time that is required for an RPC firmware update. 

GLYPH<SM590000> The RPC cards monitors power to the attached I/O enclosures. They also monitor environmental components such as power, fans, and temperature for the I/O enclosures. Environmental critical and noncritical conditions can generate EPOW events. Critical events trigger the correct signals from the hardware to the affected components to prevent any data loss without operating system or firmware involvement. Non-critical environmental events are also logged and reported. 

## 3.6.2 Line power loss 

The DS8900F uses an area of server memory as NVS. This area of memory is used to hold modified data that is not yet written to the storage drives. If line power fails, meaning that both power domain report a loss of AC input power, the DS8900F must protect that data. For a full explanation of the NVS and cache operation, see 3.2, “CPC failover and failback” on page 72 . 

## 3.6.3 Line power fluctuation 

If a power fluctuation occurs that causes a momentary interruption to power (often called a brownout ), the DS8900F tolerates this condition for approximately 20ms. If this is exceeded, the flash enclosure, CPC and other components are powered off. Independent of this, the NVDIMMs backed by the BPMs begin copying the contents of NVS to the flash memory to hold the write cache data persistently for the next power on for destaging. For many clients who use uninterruptible power supply (UPS) technology, brownouts are not an issue. UPS-regulated power is reliable, so more redundancy in the attached devices is often unnecessary. 

## 3.6.4 Power control 

Power control is modified through the HMC, which communicates sequencing information to the service processor in each CPC, RPC and iPDUs. Power control of the DS8900F can be performed by using the Service Maintenance Console Web User Interface (WUI) or by using the DS8900F Storage Management GUI or DS CLI commands. 

Figure 3-9 on page 94 shows the Power Control in the Actions menu on the Dashboard of the Storage Management GUI. 

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