[NVMe] Volatile Write Cache

Volatile write cache is a feature that allows the NVMe SSD to temporarily store data in a volatile memory buffer (usually DRAM) before writing it to the non-volatile NAND flash storage. This buffer is called the write cache or the volatile write cache.

 

The purpose of the volatile write cache is to improve the performance of write operations. When a write operation is requested, the data is first stored in the volatile write cache. The SSD then acknowledges the write operation as complete, even though the data has not yet been written to the non-volatile NAND flash storage. The data is written to the NAND flash later, when the SSD has idle time.

 

The volatile write cache improves write performance because it eliminates the need for the SSD to wait for the NAND flash to be ready before acknowledging the write operation. Without the volatile write cache, the SSD would have to wait for the NAND flash to be ready before acknowledging the write operation, which would slow down the write performance.

 

NVMe 2.0 improves the volatile write cache feature by introducing a new command called the Flush command. The Flush command is used to flush the volatile write cache and write all data in the cache to the NAND flash storage. The Flush command allows the host system to control when the data is written to the NAND flash, which can help to improve the overall performance of the system.

 

In addition to the Flush command, NVMe 2.0 also includes enhancements to the volatile write cache feature that improve the reliability of data in the cache. For example, NVMe 2.0 introduces a new feature called the Persistent Memory Region (PMR), which allows data in the volatile write cache to be written to a portion of the NAND flash that is reserved for the write cache. This helps to ensure that the data in the volatile write cache is not lost in the event of a power loss or system failure.

 

Overall, the volatile write cache is an important feature of NVMe SSDs that helps to improve the performance of write operations. NVMe 2.0 includes several enhancements to the volatile write cache that improve its performance and reliability.