Low ARC Hit Ratio

[DeletedUser88470]

I been wondering around the forum, looking for info on the ARC hit ratios, but have not found what I am looking for...
I am getting the following reports, but I am uncertain if this means that I should install more RAM?




Currently I have 16GB in my setup.

I am also a bit concerned about the temps of my CPU - do they look normal at the max 67 degrees C ?

 

[kdragon75]

ARC hit ratios are highly dependent on your use case. Also as far as your CPU, I know that model runs hot in the case you have.

 

[DeletedUser88470]

Thanks for the reply kdragon75.

I am now experiencing even lower ARC ratios - I am running plex on the server and want to install a VM with ad blocking, a VM with a video server for my cameras along with a nextcloud (plugin?? - maybe).
I can see that the Hit Ratio is dropping to 0% in some occasions... I then tried to restart...



I have installed a couple of extra fans in the case, as well as investing in a HDD case with a fan. The HDD temps became very high as well...
I could ad a aftermarket CPU cooler, and expect that this would bring down the temp by 10 degrees or so - but what would you recommend?

Thanks in advance for the advice!

 

[anmnz]

I am now experiencing even lower ARC ratios - I am running plex on the server

What data would you expect to be successfully retrieved from the ARC? You'd need to provide much more information about what you're doing for anyone to give good advice on your questions about ARC hit ratio.

If you're mainly using Plex, then I'd guess that most of the data being served up by your server is only being read once anyway. (Unless you have multiple users streaming the same content, or you're in the habit of watching the same show over and over.) That would lead to a low ARC hit ratio -- if you aren't trying to read the same data multiple times from your disks, caching it in RAM can't be effective.

 

[DeletedUser88470]

Ok, I think I understand it better now, but since my performance is very slow, would I experience better performance with more RAM from what the graphs shows?

 

[DeletedUser88470]

Let me rephrase; How would I know if I am running low on RAM and would need more? Can this be seen in the graphs?

 

[HoneyBadger]

Let me rephrase; How would I know if I am running low on RAM and would need more? Can this be seen in the graphs?

Your value for "swap" isn't 0, so yes you need more RAM.

The issue with adding jails/plugins/etc is that when FreeNAS is installed, it doesn't know that you plan to use it for anything beyond a storage server, and as such it will give as much RAM to the ARC as possible. Once you add on Plex, ad-blocking, Zoneminder, etc - those all consume RAM and FreeNAS will start having to manage the memory between ZFS and those plugins.

I would actually suggest reducing your ARC maximum value by setting the vfs.zfs.arc_max tunable in bytes to a lower value in order to leave some "available" for plugins.

As far as the hit rate itself @anmnz is on the market - ARC will cache frequently used data and unless you're rewatching the same media over and over, ARC won't assist with that.

 

[DeletedUser88470]

Terrific! This explains a lot. Thanks a lot.

 

[DeletedUser88470]

Your value for "swap" isn't 0, so yes you need more RAM

Would this be the "Used" portion under Swap Utilization?

I have now ordered another 16GB of RAM along with a better CPU cooler to hopefully extend the lifetime of the CPU a bit.

 

[HoneyBadger]

Would this be the "Used" portion under Swap Utilization?

Yes, that would be the "Used" portion.

I have now ordered another 16GB of RAM along with a better CPU cooler to hopefully extend the lifetime of the CPU a bit.

I must have missed it - what CPU is being used here that's supposedly infamous for overheating?

 

[DeletedUser88470]

I am using a E3-1270v6. I'm unaware of others having issues with it, but I would like to see my temps staying below 60 degrees, and currently it sometimes go above... This would obviously prolong the lifetime of the CPU a bit, even if it probably would be exchanged before then. I will exchange my stock Intel CPU cooler for a Noctua NH-L12S, since I have the server in my office, and I would like it to be quiet as well as being cooler than what it is now...

 

[kdragon75]

This would obviously prolong the lifetime of the CPU a bit

Unless its thermal throttling (its not at that temp) this is a bit silly and pointless.

since I have the server in my office, and I would like it to be quiet

Now that's a darn good reason!

 

[DeletedUser88470]

No, you are quite right, it won't be thermal throttling at that temp, but as a HW engineer, I find it best pratice to follow the manufacturers recommendations, aiming for a working temp of between 35 - 45 degrees.

 

[kdragon75]

No, you are quite right, it won't be thermal throttling at that temp, but as a HW engineer, I find it best pratice to follow the manufacturers recommendations, aiming for a working temp of between 35 - 45 degrees.

That's mostly warranty nonsense. As long as your not cycling rapidly, most chips are just fine 10-15 above "ideal" hard drives on the other hand... not as much.

 

[Stux]

No, you are quite right, it won't be thermal throttling at that temp, but as a HW engineer, I find it best pratice to follow the manufacturers recommendations, aiming for a working temp of between 35 - 45 degrees.

Think you’ll find the working temp is about 67C.

Those chips idle at about 35-45C.

The Noctua should work well for you.