Quantum QXS G2 Series, Hardware Installation And Maintenance Manual

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46 QXS G2 Hardware Installation and Maintenance Guide
NOTE:
Once the chassis has completed the power on sequence, the Cache Status LED displays
Solid/On (Normal), before assuming the operating state for cache purposes.
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 drives), the supercapacitor pack
provides backup power to flush (copy) data from write cache to CompactFlash 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 drives. 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 CompactFlash,
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 CompactFlash of each controller.
The Cache Status LED illuminates solid green during the boot-up process. This behavior indicates the
cache is logging all POSTs, which will be flushed to the CompactFlash the next time the controller
shuts down.
IMPORTANT: 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 CompactFlash.
Controller Failure/Single-Controller Operational
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.
Component VP SC SAS BE ASIC Host Boot Normal Reset
Blink pattern On 1/Off 7 On 2/Off 6 On 3/Off 5 On 4/Off 4 On 5/Off 3 On 6/Off 2 Solid/On Steady
Table 4 Cache Status LED – Power On Behavior
Item Display states reported by Cache Status LED during power on sequence