Can i add cache SSDs to an existing Pool?

[FumoVite]

Hello,
i would like to add two SSDs to my NAS as cache drives. How would i do that in TrueNAS-13.0-U3.1?
The only thing that *seemed* promising was a thread from 2018, but the linked documentation in there doesn't exist anymore, and i can not find the mentioned options.
www.truenas.com/community/threads/safest-way-to-add-ssd-cache-drive-in-existing-pool.62783

Specs of my NAS:
CPU: Ryzen 7 2700X
RAM: 2x8GB 3200MHz
Mainboard: Aorus B450 Pro
GPU: Nvidia K2000
SATA Controller: BEYIMEI PCI-E 4X to 6-Port
HDDs: 6 x Seagate Ironwolf ST4000VNZ06
SSDs: 1 x Patriot P300 for OS
2 x Samsung 860 Pro 250GB( the ones i would like to use for caching)
PSU: BeQuiet PurePower 11 500W

I am scared to just click "Expand Pool" or add "VDEV" without proper confirmation that it will just add the drives as cache, and not reformat everything.

Thanks in advance.

 

[sretalla]

16GB isn't nearly enough RAM to be considering L2ARC, let alone 2 drives/500GB worth of it.

I doubt "caching" works how you think it will anyway. Your best bet to improve performance is to add more RAM.

 

[FumoVite]

Ok, thank you for the response. Then i guess i will look for more ram.

 

[jgreco]

We generally don't recommend L2ARC until you have at least 64GB of ARC. This isn't a hard limit; the problem is that ARC needs cache entries to be around for some time in order to build up statistics to determine which ones would be best to put out to L2ARC. Having insufficient RAM means that what you are evicting to L2ARC is much more random. I talk about this in post #26 in this thread. It is recommended that you have somewhere between a 5:1 and 10:1 ratio of L2ARC-to-ARC, so working backwards from your 500GB of SSD's, that means 128GB of RAM would be ideal although you could probably squeeze it out of 64GB as well. This assumes your workload is amenable to caching, which is hard to know until you have at least some good amount of ARC available and you take a look at the stats.