Hybrid RAM Disk
The hybrid RAM disk uses a large buffer of volatile SDRAM memory with battery backup instead of flash memory to cache hard disk data during normal use. The buffer reduces time and energy spent accessing the hard disk. If the RAM cache needs to be filled at start-up, hybrid RAM disks may not speed the start-up process as much as flash-based hybrid disks.
Battery backup allows data to be written to permanent storage when the device is shut down, and may allow data retention in RAM for limited periods.
Frequently accessed data is stored in DRAM, while all the data is stored in hard disk. As a result, the hard disk needs to be accessed only when the processor requests data that is not frequently used.
Hybrid RAM disks are claimed to offer significantly faster read-write speeds compared to standard hard disks.
Some RAM based SSDs may be used in combination with a hard disk to create a hybrid RAM disk.
When data is written to memory, the corresponding block in memory is marked as dirty, and all dirty blocks can be flushed to the actual hard drive based on the following criteria: Time (e.g., every 10 seconds, flush all dirty data); Threshold (when the ratio of dirty data to SSD size exceeds some predetermined value, flush the dirty data); Loss of power/computer shutdown.
Read more about this topic: Hybrid Drive
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