Need some help understanding L1/L2Arc usage

[kitt001]

I'm trying to size out a new FreeNAS box (memory and L2), but I'm unclear what the current box is telling me about our L1/L2Arc. The box is used exclusively as an iSCSI backend for VMware hosts. The current version is 11.0u3 with 128GB system memory.

The numbers for Arc size and hit ratio are remarkably consistent, L2Arc is consistently 635ishGB (it's on a 1 TB SSD), and these things never really fluctuate (especially the hit ratio) ... no matter how far back I expand the graphs to see. Can someone clue me in?

 

[sretalla]

I think what that's telling you is that your ARC (RAM) is at least 10% short, which results in about 10% of the hits reaching the L2.

You seem to have a pretty stable active set of data.

With more RAM, you may see that L2ARC is entirely wasted. (and actually costs you constant writes to your SSD for no benefit).