Other Do we miss a geom_arc geom(4) L2 disk cache module/class?

[Mjölnir]

During the setup of my NAS/Home server, I encountered some flaws. One is that I miss a geom_arc(4) module -- the gcache(8) does s/th else, it would better be called geom_rs_xlt ("recordsize translator") or such:

• Since CoW/CoW suffers from write amplification, it's better not to house a VM that uses a CoW filesystem on ZFS or a ZVOL, but instead on UFS or a raw (geom(4)) partition or whole disk. But since geom(4) lacks a L2 disk cache provider, we have to decide for each VM wether to put it on rotating HDDs or fast SSDs.

A L2 ARC cache would obsolete this decision: all VMs using a CoW filesystem could live on a non-CoW device or filesystem, and a geom_arc L2 disk cache on fast NVRAM (SSDs) would keep the performance of the storage up.

What's your opinion on this topic?