Scale and Core different memory usage questions

[LarsR]

Good Morning,

After my first week of using Scale, I saw different behavior with zfs cache and memory usage between core and scale and hope someone can explain the differences.

First of all in Core the Dashboard was showing 31.9GiB total available Memory, in Scale it's only 31.3Gib. I guess that those missing 600MiB are directly allocated as System Memory and therefore are not "available" for general use - please correct me if i'm wrong.

Second is the zfs cache: In Core my cache size was roughly around ~20GiB with ~10Gib for sercvices and ~1GiB free.
In Scale i can copy files as big as 2TB to the array without the zfs cache going over 14.7GiB, services is around 5.5GiB to 6.1GiB, rest of the memory sits there unused.
I thought zfs grabs all the memory it can get so i'm wondering if this behavior is a bug.

Hope you have a nice weekend,

Lars

 

[ornias]

First of all in Core the Dashboard was showing 31.9GiB total available Memory, in Scale it's only 31.3Gib. I guess that those missing 600MiB are directly allocated as System Memory and therefore are not "available" for general use - please correct me if i'm wrong.

600MB in ZFS world is also just "margin of error", it's not even worth discussing.

I thought zfs grabs all the memory it can get so i'm wondering if this behavior is a bug.

Nope, ZfsOnLinux defaults to about 50% of available ram. so 14,7 vs 11,6 seems quite right imho.

 

[LarsR]

Thank you Ornias for the explanation.

 

[inman.turbo]

instead of scaling back ARC when a vm started which needs some of that memory, scale will just warn you, then crash your system (out of memory)

 

[Ericloewe]

@inman.turbo, I must kindly ask that the discussion not be spread out all over the place.

Scale memory utilization

There was an additional fix related to memory usage here: https://github.com/truenas/middleware/pull/9125 TL;DR you can maybe take a nightly for a spin and see if usage is stabilized. Otherwise wait for 22.02.2. Above fix (unlike charts one) shouldn't be hard to hot-patch. Will this fix...

www.truenas.com