Dell PowerVault MD3000i Hardware Owner's Manual - Page 24

Cache Functions and Features Cache Mirroring The cache mirroring function copies accepted host-write data from the primary controller to the partner controller. This action ensures that hostwrite 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. Write-Back Cache Write-back cache is a caching strategy whereby 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 will receive 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 copied to the cache of the second controller before completion status is issued to the host initiator. Write Back is enabled by default. Write-Through Cache Write-through cache is a caching strategy whereby data is written to the physical disk before completion status is returned to the host operating system. Write-through cache is considered more secure 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. NOTE: Write cache settings are not user-configurable. Power Supply and Cooling Fan Features Your RAID enclosure supports two integrated, hot-pluggable power supply/cooling fan modules. Both modules must be installed to ensure proper cooling. Each module contains two separate cooling fans. The enclosure requires at least three of the cooling fans to operate to avoid overheating. 24 About Your System