Low ARC hit ratio

[danb35]

I vaguely remember seeing some notes in the past saying that there was a bug in many earlier versions of FreeNAS, which resulted in an artificially high reported ARC hit ratio, and that this bug had been fixed (somewhere in the 9.10 series, perhaps?). Didn't pay much attention, which is probably obvious by how little detail I remember about this.

Then I took a look at the ARC stats for my server the other day, and I'm kind of surprised. I'm using my server at home, mostly SMB/CIFS file sharing, some AFP, a few NFS shares to a Ubuntu VM on another machine. I do have Plex running in a jail, along with the so-called "pirate suite" (Transmission/SABNZBd+/CouchPotato/Sonarr). The server has 128 GB of RAM, and a reported ARC size of about 80 GB right now. Hit rate is 34%:

Am I right in thinking that's kind of low? Or is that the new normal?

 

[Spearfoot]

I vaguely remember seeing some notes in the past saying that there was a bug in many earlier versions of FreeNAS, which resulted in an artificially high reported ARC hit ratio, and that this bug had been fixed (somewhere in the 9.10 series, perhaps?). Didn't pay much attention, which is probably obvious by how little detail I remember about this.

Then I took a look at the ARC stats for my server the other day, and I'm kind of surprised. I'm using my server at home, mostly SMB/CIFS file sharing, some AFP, a few NFS shares to a Ubuntu VM on another machine. I do have Plex running in a jail, along with the so-called "pirate suite" (Transmission/SABNZBd+/CouchPotato/Sonarr). The server has 128 GB of RAM, and a reported ARC size of about 80 GB right now. Hit rate is 34%:
View attachment 18272
Am I right in thinking that's kind of low? Or is that the new normal?

I vaguely remember reading those posts about the artificially high ARC hit ratio being fixed recently.

I think your system is probably within the 'New Normal' range. I get ~50% on my new FreeNAS 9.10.2-U3 server running as a VM on ESXi 6.0 w/4vCPUs, 48GB of RAM, and a 240GB L2ARC device, but I don't 'work' my system quite as hard as you do:

 

[Jailer]

It's normal.

https://forums.freenas.org/index.php?threads/solved-differing-arc-usage-in-freenas-9-10-2.48831/

 

[dlavigne]

That just got fixed in the 11.0-RC1: https://bugs.freenas.org/issues/19953.

 

[DrKK]

It's normal. High 30-ish is perfectly standard for a medium'ish RAM'med FreeNAS at home.

 

[danb35]

I'd think 128 GB would be more than "medium'ish RAM'med", but on reviewing the thread @Jailer linked, sounds entirely normal. Thanks for the pointer.

 

[DrKK]

I'd think 128 GB would be more than "medium'ish RAM'med"

Of course you're right, I assumed you had mediumish RAM. :)

 

[danb35]

(insert witty rejoinder here)

 

[Jailer]

rejoinder

Stop using words I have to look up, it's giving me a complex.

 

[Stux]

L2ARC :)

 

[danb35]

I guess I could squeeze another SSD into my chassis...

 

[toadman]

Wow. The OP had 34%? With a 128GB system?

I'm running 10VMs, mostly network infrastructure (sophos, pfsense, observium, splunk, etc.) including a plex server and separate VM for all the media apps. And some CIFS shares to network clients. I'm getting a 63.9% hit with an *8GB* system. ARC is like 5.5GB. That's way down vs the "broken" reporting from earlier.

Hmmm... Must be an entirely different effective workload.

 

[Stux]

I guess I could squeeze another SSD into my chassis...

Would be interesting to see what effect it has on your ARC stats. 128GB seems like a decent amount of RAM to start thinking about an L2ARC.

What is the recommendation, 4:1 L2ARC:ARC?