extremely slow disk I/O after updating to 12.0

Greg Marsh greg.marsh at gmail.com
Fri Jul 5 04:32:24 UTC 2019

I have been enjoying this conversation a lot.

I deal with 10's of thousands of small files daily. Since doing the sysctl
vfs.zfs.abd_scatter_enabled=0 I've noticed a massive uptick in the use of
the L2ARC and a boost to my regular processing times (this is hearsay, I
haven't done the numbers yet, but my day has been going by quicker)
My storage system a is 5 disk raidz w/ SSD L2ARC and SLOG/ZIL.

In reading the abd_scatter header file (I'm not a programmer), I'm making
an educated guess the ABD information, no longer being able to be put
wherever, needing a contiguous space of memory, has been using the L2ARC
more frequently. Please correct me if I'm wrong with this interpretation.
How file systems work is of deep interest to me and I <3 ZFS.

In any event, I have seen an uptick in the processing of these files since
doing the suggested modification.

Thank you,

On Thu, 4 Jul 2019 at 03:52, Robert Schulze <rs at bytecamp.net> wrote:

> Hi,
> Am 03.07.19 um 16:33 schrieb David Demelier:
> > Le 03/07/2019 à 13:43, Robert Schulze a écrit :
> >> we have seen a drop in I/O performance beginning with 11.2-RELEASE.
> >> Try disabling scattered ABD:
> >>
> >> sysctl vfs.zfs.abd_scatter_enabled=0
> >
> > Thanks for the answer. I'm trying this.
> >
> > Is this tunable available at boot (i.e. /boot/loader.conf) or do you put
> > it in /etc/sysctl.conf?
> I have set this tuneable in /boot/loader.conf.
> with kind regards,
> Robert Schulze
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