Product manual

VTrak E-Class Product Manual
290
• 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 73 or page 173.
Forced Read-Ahead Cache
On the VTrak 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.
Adaptive Writeback Cache
On the VTrak 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 improves performance.
To preserve the data in the cache in the event of a power failure, the subsystem
has a backup battery that powers the cache. To see an estimate of how long the
battery can power the cache, see “Viewing Battery Information” on page 73 or
“Viewing Battery Information” on page 173.
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.
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 70 or page 167.