Promise Technology VTRAK M610p Manuel télécharger pdf (Page 215)

Chapter 7: Technology Background

203

• 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 80 or page 124.

Also see “Replacing a Cache Battery” on page 184.

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Promise Technology VTRAK M610p Manuel Page 215