Owners Manual

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

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

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.

Figure 34. CompactFlash memory card

1. CompactFlash memory card

2. Controller module viewed from back

In single-controller module configurations, if the controller module has failed or does not start, and the Cache Status LED is on

or blinking, the CompactFlash needs to be transported to a replacement controller to recover data not flushed to the disk.

Storage system hardware