AMD 3D V-Cache RAM disk can read 180GB of data per second

An experiment has shown that using AMD Ryzen processors' 3D V-Cache as a RAM disc is possible. As you might've guessed, such a RAM disc is extremely fast, offering sequential read and write speeds over ten times faster than the best PCIe 5.0 SSDs.

The experiment began with an unusual snapshot taken by cooling specialist,  Albert Thomas (via Tom's Hardware), which showed a RAM disc with a claimed capacity of 508MB. This disc achieved sequential read and write speeds of approximately 178GB/s and 163GB/s in CrystalDiskMark.

Did some more testing, this time with random fill (I only used 0 fill because RND has too much write overhead, but was informed it can produce impossible results with ramdisks sometimes) – 5800X3D

But now I'm honestly even more puzzled than before 😂@ultrawide219 @itsHemu2K pic.twitter.com/4KdZz3mXdn

— Nemez (@GPUsAreMagic) November 26, 2023

Initially, the assertion was met with scepticism because it required exposing the L3 cache as a block storage device to perform the CrystalDiskMark test, and the claimed capacity was larger than the L3 cache on the processor, which has 96MB. However, there seems to be a way to use the 3D V-Cache as a RAM disc.

As explained by Nemez back in February, you can create a RAM disc out of the 3D V-Cache using OSFMount. To make it function, the RAM disc should be formatted in FAT32, and the test variables should be set to SEQ 256KB, queue depth 1, and threads 16. Moreover, the data fill should be set to zeros. Due to the nature of the system load, the procedure may require multiple attempts to achieve optimal results.

While the experiment is intriguing, it is not practical for real-world applications due to the lack of a consistent mechanism to access the 3D V-Cache. Additionally, the process is imperfect and involves trial and error. All of that aside, the amount of 3D V-Cache available is too small to be used as a reliable storage device. It could be a bit more viable on a Genoa-X EPYC processor, which comes with a maximum of 1.3GB of L3 cache.

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KitGuru says: Despite these challenges, the experiment shows promise for the future of RAM discs and 3D V-Cache technology. 

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