Promise Technology 2-Year Extended Warranty for VessR2000 RAID Head - Manual (Page 617)

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Vess R2000 Series Product Manual Promise Technologies
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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 first 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 offline. 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 offline. (See definition 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 offline” 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 field.]
◊ Advanced Battery Flash Backup enabled :
* less than 3 times backup cycle.
* [Check battery info: EstimateBackupCycle field.]