32
About PERC 6 and CERC 6/i Controllers
Virtual Disk Write Cache Policies
The write cache policy of a virtual disk determines how the controller handles
writes to that virtual disk.
Write-Back
and
Write-Through
are the two write
cache policies and can be set on virtual disks individually.
All RAID volumes will be presented as
Write-Through
(WT) to the operating
system (Windows and linux) independent of the actual write cache policy of
the virtual disk. The PERC/CERC controllers manage the data in cache
independently of the OS or any applications. Use OpenManage or the BIOS
configuration utility to view and manage virtual disk cache settings.
Write-Back and Write-Through
In
Write-Through
caching, the controller sends a data transfer completion
signal to the host system when the disk subsystem has received all the data
in a transaction.
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. The controller then writes the cached data to the storage device
in the background.
The risk of using
Write-Back
cache is that the cached data can be lost if there
is a power failure before it is written to the storage device. This risk is
mitigated by using a BBU on selected PERC 6 controllers. For information
on which controllers support a BBU, see Table 3-1.
Write-Back
caching has a performance advantage over
Write-Through
caching.
NOTE:
The default cache setting for virtual disks is
Write-Back
caching.
NOTE:
Certain data patterns and configurations perform better with a
Write-Through
cache policy.
Conditions Under Which Write-Back is Employed
Write-Back
caching is used under all conditions in which the battery is
present and in good condition.
Dell_PERC6.2_UG.book Page 32 Wednesday, June 24, 2009 6:08 PM
Содержание 6 series
Страница 1: ...Dell PowerEdge Expandable RAID Controller PERC 6 i PERC 6 E and CERC 6 i User s Guide ...
Страница 10: ...10 Contents ...
Страница 40: ...40 About PERC 6 and CERC 6 i Controllers ...
Страница 62: ...62 Installing and Configuring Hardware ...
Страница 112: ...112 Configuring and Managing RAID ...
Страница 132: ...132 Troubleshooting ...
Страница 134: ...134 Regulatory Notices ...
Страница 136: ...136 Corporate Contact Details Taiwan Only ...
Страница 156: ...156 Glossary ...