Promise Technology 2-Year Extended Warranty for VessR2000 RAID Head - Manual (Page 616)

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• Write Back – Data is written first to the cache, then to the logical drive. Better performance. Vess has a
cache backup battery to protect data in the cache from a sudden power failure.
• Adaptive Writeback – See “Adaptive Writeback Cache” below.
• Write Thru – Also “Write Through.” Data is written to the cache and the logical drive at the same time.
Safer.
If your write cache policy is set to Write Back, the write policy automatically changes to Write Thru 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
When the battery comes back online, the write policy automatically changes back to Write Back.
Also see “Viewing Battery Information” on page 119.
Forced Read-Ahead Cache
On the Vess subsystem, you can set the logical drive read cache policy to Forced Read Ahead an enable the
aggressive pre-fetch feature.
The Forced Read-Ahead cache policy setting provides predictive pre-fetching of data requests, allowing the
controller to aggressively buffer large chunks of data in cache memory to prevent frame drops on high-bandwidth
video playback. Not normally enabled for non-video applications.