ZFS ARC cache very low after a tunable, despite disabling it

[Phil1295]

Hi,

I followed this guide to enhance my TrueNAS performance:

ZFS "ARC" doesn't seem that smart...

Without yet resorting to adding an L2ARC, is there a "tuneable" that I can test which instructs the ARC to prioritize metadata? I upgraded from 16GB to 32GB ECC RAM. Yet there is zero change in this behavior. This keeps happening: I run regular rsync tasks from a few local clients, which is...

www.truenas.com

Adding the tunable

Code:

vfs.zfs.arc.meta_min=8589934592

I noticed that ZFS cache now only uses 8 GB RAM instead of quiete all the RAM

Disabling the tunable and restarting the system, I get this

I see too much free memory and no way to have ZFS properly use the free memory for cache
Is this expected ?
Why before I am sure ZFS cache was eating near all memory ?

 

[Phil1295]

Ok, after some rsync operations, the cache properly fills most free memory

 

[chuck32]

Ok, after some rsync operations, the cache properly fills most free memory

Didn't check your link in detail, however if you flushed your cache during your procedure it will not fill up automatically again.

You need to actually cache things first. Pay attention to your memory after you reboot your server, ARC will fill up when you start reading / writing data which ends up beeing cached.

 

[winnielinnie]

You need to actually cache things first.

Bingo.

One thing ZFS doesn't do (and hopefully never will do), is try to guess ahead of time what data you're going to request from the disks. Maybe in the future this whole artificial intelligence craze will infect the OpenZFS developers, and we'll have "A.I. neural network-enhanced predictive user demand" foisted upon us.

EDIT: Keep in mind the tunable will no longer exist (and hence be irrelevant), in the next version of TrueNAS Core, which will ship with OpenZFS 2.2.2.

See this thread:

ZFS "ARC" is getting smarter with version 2.2+ :smiley_face_emoji:

This is a continuation and update of this thread: https://www.truenas.com/community/threads/zfs-arc-doesnt-seem-that-smart.100423/ Looks like OpenZFS 2.2+ introduces some cleaned up and rewritten code¹ to more intelligently and gracefully handle ARC data / metadata eviction from RAM. It's such...

www.truenas.com

 

[Phil1295]

Bingo.

One thing ZFS doesn't do (and hopefully never will do), is try to guess ahead of time what data you're going to request from the disks. Maybe in the future this whole artificial intelligence craze will infect the OpenZFS developers, and we'll have "A.I. neural network-enhanced predictive user demand" foisted upon us.

EDIT: Keep in mind the tunable will no longer exist (and hence be irrelevant), in the next version of TrueNAS Core, which will ship with OpenZFS 2.2.2.

See this thread:

ZFS "ARC" is getting smarter with version 2.2+ :smiley_face_emoji:

This is a continuation and update of this thread: https://www.truenas.com/community/threads/zfs-arc-doesnt-seem-that-smart.100423/ Looks like OpenZFS 2.2+ introduces some cleaned up and rewritten code¹ to more intelligently and gracefully handle ARC data / metadata eviction from RAM. It's such...

www.truenas.com

Yes, I saw it. I just hope it is as good as this tunable since it is only a priority ponderation whith unknown exact behavior as of the size of cache before it gets emptied. They removed the current tunable in current openzfs