When a controller is shut down or otherwise rendered inactive—its Link Status LED remains illuminated— falsely indicating that the
controller can communicate with the host. Though a link exists between the host and the chip on the controller, the controller is not
communicating with the chip. To reset the LED, the controller must be power-cycled.
Cache status LED details
This section describes the behavior of the LEDs during powering on and off and cache flushing.
Power on/off behavior
During power on, discrete sequencing for power on display states of internal components is reflected by blinking patterns displayed by the
Cache Status LED.
Table 9. Cache Status LED – power on behavior
Item
Display states reported by Cache Status LED during power on sequence
Display
state
0
1
2
3
4
5
6
7
Compone
nt
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
Once the enclosure 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 disk), 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
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 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 Power
On Self Tests (POSTs), which will be flushed to the CompactFlash 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 CompactFlash.
CompactFlash
During a power loss or controller failure, data stored in cache is saved off to non-volatile memory (CompactFlash). The data is restored to
cache, and then written to disk after the issue is corrected. To protect against writing incomplete data to disk, the image stored on the
CompactFlash is verified before committing to disk. The CompactFlash memory card is located at the midplane-facing end of the controller
module. Do not remove the card; it is used for cache recovery only.
30
Storage system hardware
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