why FreeNAS only use 16(total is 20GB) memory?

[fisherwei]

I already tried autotune.

 

[SweetAndLow]

Auto tune is probably what caused it to do that. Remove the auto tune settings.

 

[Bidule0hm]

In fact I've also some RAM always free (2.4 GB free and 11.5-12 Gb of ARC on 16 GB installed) and I'm curious to know why the free space isn't used for the ARC (or other things).

 

[cyberjock]

Some RAM is never used because when an application needs more memory it needs to be immediately available. It takes time for ZFS to free RAM, and if an application needs RAM faster than ZFS can release it.... bad things can happen.

My 32GB system typically has 2-3GB of RAM free.

Also keep in mind that:

1. ZFS doesn't use RAM unless it thinks there's something to be gained from a performance perspective. It's pretty liberal with using RAM until the system starts to run out.
2. Tunables and such change the behavior.. and autotune is *supposed* to set some conservatively hard limits.

Because of #2, you're probably creating this problem on your own. There's a reason we don't recommend you check the box.

 

[Bidule0hm]

Ok, thanks ;)

 

[Knowltey]

If I remember correctly the default setting for ARC size is somewhere between 70 and 80 percent of total RAM, so 16/20 seems to be about right.

 

[fisherwei]

actually, before I checked autotune, it stopped at 16G already.
that is why I try to use autotune.

Can I adjust some tunable parameter, let ARC use more mem(maybe 95% or 90%?)