User Manual

590
Vess R2000 Series Product Manual Promise Technologies
AdAPtive writebAck cAche
On the Vess subsystem, you can set the logical drive write cache policy to Write Thru or Write Back.
If you set the write cache policy to Write Back, your data is rst written to the controller cache, and later to
the logical drive. This action is conducted to improve performance. In order to preserve the data in the cache in
the event of a power failure, the subsystem has a backup battery that provides continuous power to maintain
the cache. To see an estimate of how long the battery can power the cache, see “Viewing Battery Information”
on page 119.
The Adaptive Writeback Cache feature protects your data by changing the write cache settings while the cache
backup battery is ofine. When all of the following conditions occur:
•
ThelogicaldrivewritepolicyissettoWriteBack.
• TheAdaptiveWritebackCachefeatureisenabled.
• Thecachebackupbatterygoesofine.(SeedenitioninNotebelow)
The write policy automatically changes to Write Thru. When the battery comes back online, the write policy
automatically changes back to Write Back.
To enable the Adaptive Writeback Cache option, see “Making Controller Settings” on page 113.
Notes
The condition “cache battery goes ofine” can be due to one of the
following circumstances:
• Battery not installed.
• Battery remaining capacity is not enough to keep data, outcome depends if
Advanced Battery Flash Backup is enabled or disabled :
◊ Advanced Battery Flash Backup disabled:
* less than 72hrs (48hrs for 16GB of memory).
* [Check battery info: EstimateHoldTime eld.]
◊ Advanced Battery Flash Backup enabled:
* less than 3 times backup cycle.
* [Check battery info: EstimateBackupCycle eld.]