[zfs-discuss] ZFS eating up all 16 GB RAM when combining 4k blocksize ZVOL with XFS

Bzzzz lazyvirus at gmx.com
Tue Nov 13 15:13:49 EST 2018

On Tue, 13 Nov 2018 20:31:48 +0100
Omar Siam via zfs-discuss <zfs-discuss at list.zfsonlinux.org> wrote:

> Right now I use the Ubuntu 18.04.1 with all updates.

Hum, I do not trust very much pale copies (of Debian)…

> That makes  a
> Linux 4.15 with patches,

Unless many people also use it without any known problem (especially
yours) this might be a source of worry : the trudububu "way" being to
introduce far too easily non-stable proven package, sometimes with
unpredictable results (I'll _never_ use that for a production server!)

ie: the 4.15.x kernel series did not even appear in Debian stable
(stretch) nor it did into debian-backports (the almost next stable
branch) and I remember reading rapidly an article about 4.15.x not being
suitable in stable installations (don't remember why) which can explain
why it did not made it into debian.

In fact, it jumped directly from 4.9 to 4.17-bpo, 4.18-bpo & 4.19-rc7
there IS indeed a reason for that somewhere…

> a zfs 0.7.5 with patches for critical fixes (at least I hope so)

The latest stable being 0.7.11 did you try to install it from scratch?
[correction, you speak about it later]
and/or did you try to downgrade it (if possible) to see what's happen?
ad the same for the kernel ?

> and libaio 0.3.110.

The same here.

> I saw the effect also using a
> 4.18 kernel with zfs 0.7.11 on Ubuntu 18.04.1. I didn't try the 0.7.11
> dkms yet.

This may be your best move as:
* 4.18 seems stable enough to emerge into debian-backports,
* At the dev point where ZFS stands, every new release contains
   important fixes and modifications that justify the hop to it.

> > Did you carefully review all involved configuration files on both
> > machines, and are those hardwares identical ?  

> The configuration between iSCSI initiator and target are not
> identical. The iSCSI initiator is not identical in hardware to the
> target. The initiator runs an Ubuntu 4.15 kernel.

Once again that kernel…

> The hardware of the machine running ZFS is identical between the local 
> running test, LIO/iSCSI target and SCST 3.3.x target and freenas. It
> is the same machine. I just change the software.
Which one?
Can you downgrade to the same version that runs correctly on the other
machine ?

> It is a Core i3 6300
> based machine with 16 GB of ECC RAM and a server mainboard with an
> C232 chipset so ECC is really used. It has a 10 GB/s Intel network
> card for iSCSI.

Finally, I'd say:

1) have a look at the kernel, as it is the part that looks
     the most suspicious IMHO - have a look at:
	(NB: TL;DR, only the titles and a word here and there)

2) then the software version you're talking about just above.

4 to 1 that it is a kernel issue :)


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