Re: close() taking minutes (ZFS related)

On Jan 23, 2023, at 5:54 AM, Peter <pmc@citylink.dinoex.sub.org> wrote:

> It seems I have found the reason for the strange behaviour: it is
> dedup.
> 
> The pool is configured to use dedup, because it carries all my jail OS
> installation, which are very similar. But dedup makes no sense on
> database filesets, and apparently it has very bad effects on real
> workload: it creates immense write-amplification (about factor 4)
> and probably other bad effects (memory is not the issue here).
> 
> I don't think it should lockdown the entire pool, but it is
> understandable that it creates a logical relation between the
> different filesets.


Note that "dedup" is a fileset-level property and so if the database filesets are poor candidates for deduping you should be able to set dedup to "off" for them to mitigate their bad impact on the system.

Even though dedup is a fileset-level property, enabling dedup on any fileset can have major impact system-wide (due to large resource consumption) and so should be done with due diligence.

Cheers,

Paul.