Owners Manual

CAUTION: For single-controller module configuration only, to preserve the existing data stored in the
CompactFlash, you must transport the CompactFlash from the failed controller module to the replacement
controller module. This procedure is outlined in the Dell EMC PowerVault ME4 Series Storage System Owner's
Manual within the procedure for replacing a controller module. Failure to use this procedure will result in the
loss of data stored in the cache module. The CompactFlash must stay with the same enclosure. If the
CompactFlash is used/installed in a different enclosure, data loss/data corruption will occur.
NOTE: In dual-controller module configurations featuring one healthy partner controller module, there is no need to
transport the CompactFlash from the failed controller module to the to the replacement controller module. The cache is
duplicated between the controller modules, provided that volume cache is set to standard on all volumes in the pool owned
by the failed controller module.
Supercapacitor pack
To protect controller module cache in case of power failure, each controller enclosure model is equipped with supercapacitor
technology, in conjunction with CompactFlash memory, built into each controller module to provide extended cache memory
backup time. The supercapacitor pack provides energy for backing up unwritten data in the write cache to the CompactFlash, in
the event of a power failure. Unwritten data in CompactFlash memory is automatically committed to disk media when power is
restored. In the event of power failure, while cache is maintained by the supercapacitor pack, the Cache Status LED blinks at a
rate of 1/10 second on and 9/10 second off.
Controller failure when a single-controller is
operational
The following information applies to 2U single controller enclosures when the controller fails. The following information also
applies or 2U and 5U dual-controller enclosures when one of the controllers is down and the other controller fails.
Cache memory is flushed to CompactFlash in the case of a controller failure or power loss. During the write to CompactFlash
process, only the components needed to write the cache to the CompactFlash are powered by the supercapacitor. This process
typically takes 60 seconds per 1Gbyte of cache. After the cache is copied to CompactFlash, the remaining power left in the
supercapacitor is used to refresh the cache memory. While the cache is being maintained by the supercapacitor, the Cache
Status LED blinks at a rate of 1/10 second on and 9/10 second off.
NOTE:
Remove the CompactFlash memory card only if recommended by Dell EMC technical support.
Transportable cache only applies to single-controller configurations. In dual-controller configurations featuring one healthy
partner controller, there is no need to transport failed controller cache to a replacement controller because the cache is
duplicated between the controllers, provided that the volume cache is set to standard on all volumes in the pool owned by
the failed controller.
Cache status LED – corrective action
If the controller has failed or does not start, check if the Cache status LED is on or blinking.
Table 10. LEDs: Rear panel Cache Status
Status Action
Cache status LED status is off, and the controller
does not boot.
If the problem persists, replace the controller module.
Cache status LED is off, and the controller boots. The system has flushed data to disks. If the problem persists, replace
the controller module.
Cache status LED blinks at a 1:10 rate - 1 Hz, and the
controller does not boot.
You may need to replace the controller module.
Cache status LED blinks at a 1:10 rate - 1 Hz, and the
controller boots.
The system is flushing data to CompactFlash. If the problem persists,
replace the controller module.
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