Question RE RAM Requirements vs Performance

[ghackett]

Hey all, so I'm building my first FreeNAS box as we speak. I'm aiming to build 1 zfs2 volume with encryption for personal home/media storage & streaming (with the plex media server pbi).

My question is this...
I'm hoping to use all 8 sata ports on my mobo each with a 4tb red drive giving me 32gb raw storage and ~21TB usable storage (I understand this is not an ideal # of drives but AFAIK thats only a real perf hit in enterprise production environments, please correct me if I'm wrong here). However, my mobo and cpu (SuperMicro X10SAT - http://www.newegg.com/Product/Product.aspx?Item=N82E16813182830 and Xeon E3-1220V3 - http://www.newegg.com/Product/Product.aspx?Item=N82E16819116907) only support 32GB of RAM (which I plan on maxing out with ECC memory). While this is (barely) within the threshold of 1GB per TB raw storage in the pool, it does not leave the extra 1-2GB for FreeNAS or whatever might be needed by the Plex Media Server pbi.

So the question is, how badly does perf degrade if I'm a few GB shy of the recommended RAM? In my use-case (home use / media streaming) would I see enough of an impact to warrant using only 7 drives instead of 8 (which would still meet my storage needs for now, just wouldn't be ideal). Also does encryption add any requirements to RAM, or is that just more CPU load?

Thanks in advance

 

[Michael Wulff Nielsen]

As far as I know the memory requirement is not an absolute rule. You do need 8 gb of memory, but since you are running a home/low client scenario you could probably make do with 8. I am sure that 16 will be more than enough.

I have 16 gb and my personal nas never goes above 8gb memory usage even with plex running.

 

[cyberjock]

For home use and for CIFS sharing 16GB will probably be fine for you. I'd probably by 2x8GB sticks and stick with those. If performance isn't satisfying then buy another 2x8GB sticks. I'd guess you will probably be okay with 16GB of RAM. But if you either add more disks or get bigger disks you'll almost certainly be forced to upgrade to 32GB of RAM.

 

[jgreco]

The RAM sizing guide in the hardware requirements is deliberately a little vague because no actual hard ruleset exists. Among the vagarities, I was careful not to suggest if the 1GB/1TB guideline means per TB raw storage, or per TB usable, or even per TB used. Each interpretation is valid under certain circumstances. and yet even the most conservative interpretation of "per raw TB" is capable of underestimating RAM requirements for many workloads, while a home user might successfully have a 6 * 4TB in RAIDZ2 on 8GB RAM... just a bit slow.