DELL MD3220 사용자 설명서

Planning: RAID Controller Modules

Cache mirroring function copies accepted host-write data from the primary 

controller to the partner controller. This action ensures that host-write data is 

safely mirrored to the partner controller before successful completion status is 

returned to the host. If a controller fails, the surviving controller safely retains 

all mirrored data. Cache mirroring is enabled by default.

In Write-back Cache, write operations result in a completion signal being 

sent to the host operating system as soon as the cache receives the data to be 

written. The target physical disk receives the data at a more appropriate time 

in order to increase controller performance. In dual-active controller 

configurations with Write-back Caching enabled, the write data is always 

mirrored to the cache of the second controller before completion status is 

issued to the host initiator. Write-Back Cache is enabled by default unless 

cache mirroring is disabled.

In write-through cache, data is written to the physical disk before completion 

status is returned to the host operating system. Write-through cache is 

considered more robust than write-back cache, since a power failure is less 

likely to cause loss of data. The RAID controller automatically switches to 

write-through if cache mirroring is disabled or if the battery is missing or has a 

fault condition.

book.book  Page 34  Monday, June 21, 2010  11:00 AM