Write Cache Policy; Adaptive Writeback Cache - Promise Technology VTRAK E310f Product Manual

• Read Ahead – The read cache and the read-ahead feature are enabled.
Read-ahead anticipates the next read and performs it before the request is
made. Can increase read performance.
• No Cache – The read cache is disabled.

Write Cache Policy

• Write Back – Data is written first to the cache, then to the physical drive.
Better performance. VTrak has a cache backup battery to protect data in the
cache from a sudden power failure.
• Write Thru – Also "Write Through". Data is written to the cache and the
physical drive at the same time. Safer.
If Write Policy is set to Write Back, and 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.
If Write Policy is set to Write Back, and the Adaptive Writeback Cache feature is
enabled, the Write Policy will remain at Write Back even when the battery is
offline. Any data in the controller cache will be lost in the event of a power failure.

Adaptive Writeback Cache

On the VTrak subsystem, you can set the logical drive write cache policy to Write
Through 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 physical 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 up to 72 hours.
Normally, if the cache backup battery is not present or the battery is being
reconditioned, your logical drive write cache policy is automatically set to Write
Through, so no data is stored in the controller cache. This action slightly reduces
performance but avoids data loss in the event of a power failure. When a battery
is installed or finishes reconditioning, the write cache policy is automatically reset
to Write Back.
The Adaptive Writeback Cache option enables you to set your logical drive write
cache policy to Write Back, even if no cache backup battery is present or the
battery is being reconditioned. This action improves performance but also risks a
loss of data in the event of a power failure.
To enable the Adaptive Writeback Cache option, click on the Controller Settings
tab. See "Making Controller Settings" on page 101 or page 147.
Also see "Replacing a Cache Battery" on page 215.
Chapter 7: Technology Background
237