Cache status behavior
If the LED is blinking evenly, a cache flush is in progress. When a controller module loses power and write cache is dirty
(contains data that has not been written to disk), the supercapacitor pack provides backup power to flush (copy) data from
write cache to memory. When cache flush is complete, the cache transitions into self-refresh mode.
If the LED is blinking momentarily slowly, the cache is in a self-refresh mode. In self-refresh mode, if primary power is restored
before the backup power is depleted (3–30 minutes, depending on various factors), the system boots, finds data preserved
in cache, and writes it to disk. This means the system can be operational within 30 seconds, and before the typical host I/O
time-out of 60 seconds, at which point system failure would cause host-application failure. If primary power is restored after
the backup power is depleted, the system boots and restores data to cache from the system eMMC, which can take about 90
seconds. The cache flush and self-refresh mechanism is an important data protection feature; essentially four copies of user
data are preserved: one in controller cache and one in the eMMC of each controller. The Cache Status LED illuminates solid
green during the boot-up process. This behavior indicates the cache is logging all Power On Self Tests (POSTs), which will be
flushed to the eMMC the next time the controller shuts down.
NOTE:
If the Cache Status LED illuminates solid green—and you wish to shut down the controller—do so from the user interface,
so unwritten data can be flushed to eMMC.
Controller failure when a single-controller is operational
The following information applies to 2U and 5U dual-controller enclosures when one of the controllers is down and the other
controller fails.
Cache memory is flushed to eMMC in the case of a controller failure or power loss. During the process of writing to eMMC, only
the components needed to write the contents of the cache to the eMMC are powered by the supercapacitor. After the cache is
copied to eMMC, 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.
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 8. 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.
Cache status LED blinks at a 1:1 rate - 2 Hz, and the
controller does not boot.
You may need to replace the controller module.
Cache status LED blinks at a 1:1 rate - 1 Hz, and the
controller boots.
The system is in self-refresh mode. If the problem persists, replace the
controller module.
Storage system hardware 25
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