Dell PowerEdge RAID Controller 10 User’s Guide PERC H345, H740P, H745, and H840 Series Controllers

Controller cache

The H740P, H745, H745P MX, and H840 cards contain the local DRAM on the controllers. This DRAM can cache I/O operations per second for Write Back, Read Ahead virtual disks to improve the performance.

NOTE: Virtual disks consisting of SSDs may not see a difference in performance using controller cache and may benefit by Fastpath.

I/O workload that is slow to HDDs, such as random 512 B and 4 KB, may take some time to flush cached data. Cache is flushed periodically but for configuration changes or system shutdown, the cache is required to be flushed before the operation can be completed. It can take several minutes to flush cache for some workloads depending on the speed of the HDDs and the amount of data in the cache.

The following operations require a complete cache flush:

CAUTION:Reduce or stop the running workload before performing any of these operations.

Configuration changes (add or delete VDs, VD cache setting changes, foreign configuration scan, and import)
System reboot or shutdown
Abrupt power loss causing Cache preservation

NOTE:The iDRAC or OpenManage periodically scans for the foreign configurations when the foreign disks are present, these actions may degrade the performance periodically. If a foreign disk is present, it is recommended to import, clear, or remove the foreign disk to prevent an impact on the performance.

Dell PowerEdge RAID Controller 10 User’s Guide PERC H345, H740P, H745, and H840 Series Controllers

Controller cache

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