Dell OpenManage Server Administrator Managed Node for Fluid Cache for DAS Manuel d'utilisateur télécharger pdf (Page 96)

96 Controllers

Write Policy

Does my controller support this feature? See

Supported Features

The write policies specify whether the controller sends a write-request

completion signal as soon as the data is in the cache or after it has been

written to disk.

•

Write-Back

—When using write-back caching, the controller sends a

write-request completion signal as soon as the data is in the controller

cache but has not yet been written to disk. Write-back caching may

provide improved performance since subsequent read requests can more

quickly retrieve data from the controller cache than they could from the

disk. Write-back caching also entails a data security risk, however, since a

system failure could prevent the data from being written to disk even

though the controller has sent a write-request completion signal. In this

case, data may be lost. Other applications may also experience problems

when taking actions that assume the data is available on the disk.

NOTE: Storage Management does not allow you to select the Write-Back

policy for controllers that do not have a battery. The only exception are PERC

S100 and S300. This restriction protects a controller without a battery from the

loss of data that may occur in the event of a power failure. On some

controllers, the Write-Back policy may be available in the controller BIOS

even though it is not available in Storage Management.

•

Force Write Back

—When using force write-back caching, the write cache

is enabled regardless of whether the controller has a battery. If the

controller does not have a battery and force write-back caching is used,

data loss may occur in the event of a power failure.

•

Write Back Enabled

—When using write-back enabled caching, the

controller firmware disables the write cache if it does not detect the

presence of a charged battery over a specified period of time. For example,

on some controllers, the write cache is disabled if the firmware cannot

detect a charged battery within 72 hours.

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Dell OpenManage Server Administrator Managed Node for Fluid Cache for DAS Manuel d'utilisateur Page 96