LSI® MegaRAID® CacheVault™ Technology
Providing access to write-back cache is one of the many benefits of a hardware RAID controller card. Write-back cache improves application performance by storing write data to high performance cache memory during periods of heavy use. When there is a break in user requests the data is then written from the cache memory to the array.
During normal write-back operation, data is written to cache (DRAM), the IO is acknowledged as “complete” to the application that issued the write, and later the write is flushed to disk. If power is lost while write-back cache is enabled, the writes in DRAM may be lost. And since the controller has already acknowledged the IOs as complete, the application is unaware of the data loss.
To minimize this risk, Enterprise RAID controllers equipped with cache typically offer a battery back-up (BBU) option. The purpose of the battery is to provide power to the controller in the event that the power from the server is interrupted. This protects the data in the cache until power to the server can be restored and cache data written to disk.
While generally effective, BBUs may require maintenance, special handling and protect cache data for a limited time. CacheVault technology, providing flash-based cache protection for MegaRAID 6Gb/s SATA+SAS RAID controllers, offers a greener, lower total cost cache protection solution without the drawbacks of a BBU.
CacheVault technology provides RAID controller cache protection using NAND flash memory and a supercapacitor. In the event of a power or server failure, CacheVault technology automatically transfers cached data from the DRAM cache to flash. Once power is restored, the data in the NAND flash is copied back into cache until it can be flushed to the disk drives. This technology eliminates the need for Lithium-ION battery backups that are traditionally used to protect cache memory on PCI RAID controllers.
Go Green and Save
Using NAND flash eliminates the need to dispose of the LithiumION batteries typically found in today’s BBUs. These batteries are a potential risk to the environment and many communities require that they be disposed of properly. This is something that will have to be done every time the battery is replaced during the course of the controller’s life. By eliminating the need for these batteries, the risk to the environment and the cost of disposal can be avoided.
CacheVault Technology vs Standard Battery Backup
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