Owners Manual

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.
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
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Storage system hardware