Autotune settings negative Read impact

[Rand]

I am wondering which autotune settings did have negative impact on read speed?

I've found it mentioned eg by Cyberjock but without listing the actual variables but couldnt find which ones actually cause that problem.
Neither could i find which values are being set (as in documentation) and a discussion of them...

I checked autotune.py but despite the comments in there its not really explaining things;)

 

[Yatti420]

Shouldn't use autotune unless you have the system to do so..

 

[cyberjock]

So the problem was that with really big systems(think 128GB of RAM+) ZFS was getting more and more aggressive with its RAM usage. The more RAM you had the more agressive it got. It was causing kernel panics because ZFS used all the RAM and the system would become unstable. The solution would appear to be "add more RAM" for the admin looking at the problem. But, since ZFS got more and more agressive with more RAM, you actually made the problems worse!

So Autotune was created to prevent this runaway condition. It didn't really work as well as had been hoped, and it was basically added then abandoned. It's basically deprecated and shouldn't really be used.

All of the autotune settings, if they deviate from the defaults(because one used to increase NIC memory blocks or something, but now the default is bigger anyway), will hurt performance. This is because of what Autotune was supposed to be used for.

The tl;dr version is that realistically nobody should be using autotune if you care about performance and even then, not unless you have the condition I explained above. And that runaway condition doesn't exist on ZFS anymore, so unless you are using older FreeNAS versions, you really shouldn't be even using it.

 

[eduardoalvim]

So, generally speaking, if I have autotunes enabled (as I do on my 8.4.x system) I just need to untick it?


Enviado do meu iPhone usando o Tapatalk

 

[cyberjock]

So, generally speaking, if I have autotunes enabled (as I do on my 8.4.x system) I just need to untick it?


Enviado do meu iPhone usando o Tapatalk

There is no 8.4.x releases.

But, assuming you are still using FreeNAS, you'll need to read the information in the manual for disabling autotune. It's not as simple as unchecking the box. You will need to delete the tunables and sysctls and reboot. ;)

 

[Yatti420]

Is autotune variables still being tweaked by freenas dev or should it just be completely removed? I guess with some work it could be useful for machines with 100+gb of ram.. That's a whole nother world with a system like that..

 

[eduardoalvim]

My bad, I'm using 8.3.1 (writing far from office) :). Thanks for the tip.

 

[Rand]

In my particular case i have set some variables for 10GBe performance and see better writes than reads and thought this was the same issue that caused the problem on autotune.
I will put it in another thread, then this one can focus on autotune.