How much ram for zfs filesystem?

[Ronald Q]

Hi, i realized when you use zfs in a pool or main array the system allocate some part of my ram to this endevour.

 

I run a pretty old z170 chipset mother board, i7-2700k cpu (4C 8T), and im limited to 16Gb of hardware ram. My cpu allows for 32. But the motherboard does not.

 

Actually my unraid os allocate 2GB from the total 16GB to the zfs system. I suppose is a type of cache or something. Not sure about how it works under the hood.

 

• Can i increase the allocated ram to zfs? how?
• is 2gb not enough?
• can i get bad performance for the lack of ram allocated to ZFS?

 

Thanks

[JorgeB]

By default Unraid sets 1/8 of installed RAM as ARC max, but you can change that:

 

https://docs.unraid.net/unraid-os/release-notes/6.12.0/#zfs-pools

 

As for how much to set, give it as much as you can afford, zfs will perform better with more RAM for the ARC, also note that the ARC will only use the free RAM available, you just set a max, but in some cases, it may not be quick enough to release the RAM if needed quickly, like when starting a VM for example, so need to account for that.