I use TrueNAS to store weekly backups and other data for my systems at home, no VMs or other apps. Last time I transferred a 700GB system backup from another PC, I noticed the available RAM in my server’s GUI was dwindling to almost nothing, then stopped the transfer. I’m using 8x 4TB drives in a …

[image] Lylat1an: I noticed the available RAM in my server’s GUI was dwindling to almost nothing. That’s normal–your system has the RAM, so ZFS ought to use it. For your pool, 64 GB are enough. More is likely to be better, but check your ARC stats in the Reporting pages. But you don’t need …

[image] dan: you don’t need more RAM based on what you’ve described. So I could benefit from more? How much more would be ideal? My motherboard can take up to 256GB.

[image] Lylat1an: So I could benefit from more? Maybe. What do your ARC statistics look like? The likelihood that you can benefit significantly with 64 GB of RAM and 20 TB of usable pool capacity is pretty small. But, again, TrueNAS has instrumentation to help you out here. What makes you…

I restarted the transfer and the ARC seems to be holding steady at 57GB, and there’s 2-3GB not being used. I was afraid the ARC would take more and run out. Still, would the system be happier if I added more RAM?

[image] Lylat1an: Still, would the system be happier if I added more RAM? I guess, but probably not measurably. For the third time, what do your ARC statistics look like?

I don’t think your system would operate much different with more RAM if your measure is writing a single large file. Let me toss in a wrench… why is the ARC filling up so quickly? You are not able to write data faster than your current pool layout. If there is a transfer rate issue, fix the pool …

The transfer rate averages 200MB/s when writing to the pool. Do you think that can be improved?

I restarted the transfer and it looks like this after about 12 minutes. [ARC]

That is absolutely what it is supposed to look like. What would you suggest the system do with that RAM instead? Unused RAM is wasted RAM. If you add e.g. VMs to your configuration they will get their configured share of your physical memory but the ARC will always fill up the rest sooner or later.…

I need to increase my RAM for ZFS, but by how much?

TrueNAS General

Stux May 7, 2025, 11:38pm 6

I guess, because if OP had called the thread “should I increase my RAM for ZFS” he would’ve triggered @winnielinnie

Topic		Replies	Views
Adding a NVMe drive as a L2ARC cache drive? TrueNAS General	3	208	July 20, 2025
ZFS cache preventing app from getting allocated memory it needs Apps and Virtualization SCALE , ZFS	9	312	November 14, 2025
Memory issue while transferring data between two pools: Purging GPU Memory TrueNAS General SCALE	4	374	May 22, 2024
ARC memory keeps increasing TrueNAS General	17	298	September 27, 2024
Tips for beginners: how much RAM is needed? TrueNAS General Hardware	13	7164	April 29, 2025

I need to increase my RAM for ZFS, but by how much?

Related topics