What is persistent cache and why is it important?
Persistent cache is counted and considered actual storage capacity and cache isn't. A cache is considered temporary, so in the case of a system reboot or crash, the data held in a cache is gone. Vendors back up the data on a cache with a battery, usually called battery backup, in order to help a system come back in a healthy state. But if the battery is not on or loses power, the data is lost. Also, some vendors may go a step further and flush data to battery-backed DRAM as additional protection against data loss, just like what you would find on a controller card or storage controller when data is flushed to battery-backed cache in case of failure.
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Persistent cache means information is stored in "permanent" memory, so data is not lost after a system restart or system crash as it would be if it was stored in cache memory. This is very important if you plan to use flash memory as a storage tier and need that data to be stored with data protection and enterprise data services.
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