Dell PowerEdge RAID Controller H700 Manual de usuario descargar pdf (Pagina 87)

Configuring and Managing RAID 87

Write Policy Write Policy specifies the controller write policy. You can set the write

policy to Write-Back or Write-Through.

In Write-Back caching, the controller sends a data transfer

completion signal to the host when the controller cache has received

all the data in a transaction.

NOTE: If a Battery Backup Unit (BBU) is present, the default cache

setting is Write-Back. If no BBU is present, the default cache policy

default setting is Write-Through.

NOTE: If Write-Back is enabled and the system is quickly turned off and

then on, the controller may pause as the system flushes cache memory.

Controllers that contain a battery backup default to Write-Back caching.

In Write-Through caching, the controller sends a data transfer

completion signal to the host when the disk subsystem has received

all the data in a transaction.

Read Policy Read-Ahead enables the read ahead feature for the virtual disk.

You can set the parameter to Read-Ahead, No-Read-Ahead,

or Adaptive. The default is Adaptive-Read-Ahead.

Read-Ahead specifies that the controller uses Read-Ahead for the

current virtual disk. Read-Ahead capability allows the controller to

read sequentially ahead of requested data and store the additional

data in cache memory, anticipating that the data is required soon.

No-Read-Ahead specifies that the controller does not use read ahead

for the current virtual disk.

Adaptive specifies that the controller begins using Read-Ahead if the

two most recent disk accesses occurred in sequential sectors.

If all read requests are random, the algorithm reverts to

No-Read-Ahead; however, all requests are still evaluated for

possible sequential operation.

Table 6-2. Virtual Disk Parameters and Descriptions

(continued)

Parameter Description

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Dell PowerEdge RAID Controller H700 Manual de usuario Pagina 87