NVMe characteristics important to PrimoCache?

[nicoloks]

Hi All,

Looking to purchase a larger NVMe PCIe 4 disk to use as my PrimoCache disk. I had no idea previously how much detail in drive characteristics and capabilities there were to dig into here. NVMe controller, DRAM and NAND speeds are all huge factors in determining performance. No point having the fastest NAND if the controller can't supply the throughput, likewise no use having enormous NAND capacity if there is no DRAM to cache the I/0 as otherwise speeds can fall to SATA3 speeds (or less) as the disk gets fuller.

My first question is, what sort of performance is important to PrimoCache? Is random IO performance the most important, or does PrimoCache read/write from L1 and spinning disk to/from L2 cache in sequential reads and writes?

Second question. I've been told you should only partition NVMe drives to 80% of their capacity to ensure best performance as the drive fills and also to prevent excessive wear. Is this true and does this present any considerations for PrimoCache?

[Nick7]

Firstly - PrimoCache is a bit silly with filling L2 cache, as L2 (read) cache is filled by reading from disks, and not by using data in L1 cache. Write cache (if using) is different matter.

As for using 80% - some suggest is as PrimoCache does not support TRIM. So leaving extra free space may help with internal garbage collection on SSD/NVMe.

[Support]

My first question is, what sort of performance is important to PrimoCache? Is random IO performance the most important, or does PrimoCache read/write from L1 and spinning disk to/from L2 cache in sequential reads and writes?

The sequential and random read/write performance of SSD are both important to the L2 cache performance. Relatively speaking, the SSD's random read/write performance is more important.

[petroben]

Hello,

For PrimoCache, random IO performance is generally more critical than sequential performance. PrimoCache optimizes system performance by caching frequently accessed data, and often, random IO occurs in real-world scenarios.

Regarding partitioning NVMe drives to 80% capacity, while it's true that leaving some space unallocated can help maintain performance and extend the lifespan of the drive due to wear leveling, it might not have a direct impact on PrimoCache considerations. PrimoCache manages caching between different layers (L1 and L2) and doesn't necessarily require specific drive partitioning. However, it's always a good practice to ensure adequate free space on any storage device for optimal performance and longevity.

Best regards.