Zfs heavy io writing | zfskern txg_thread_enter

Michelle Sullivan michelle at sorbs.net
Fri Feb 19 13:06:29 UTC 2016

Steven Hartland wrote:
> On 19/02/2016 11:58, Michelle Sullivan wrote:
>> Niccolò Corvini wrote:
>>> Hi, first time here!
>>> We are having a problem with a server running FreeBsd 9.1 with ZFS on a
>> You should upgrade to a supported version first...  9.3 would probably
>> be the best (rather than 10.x) as it's still supported and uses the same
>> ABI (ie you should need to reinstall all your ports/packages - though
>> you should because it sometimes breaks things - at least check for
>> broken things :) .)
>> If you're not familiar "freebsd-update -r 9.3-RELEASE upgrade" will help
>> you do it without too many problems.
> 9.3 is still ancient, and while "supported" its not in active
> development, and to be blunt no one will be interested in helping to
> diagnose any actual issue on something so old.

So supported is not really supported... Is that an official position?

> 10.x has a totally different ZFS IO scheduler for example, so its
> differently for most workloads.

But the user is on 9.x not 10.x and 10.x changes a lot more than just
the ZFS IO scheduler.  If this is a production machine, then an upgrade
to 9.3 may be easier as it would require less regression testing....  Or
is this another case of people don't run FreeBSD in production
environments so it doesn't matter...?

>>> single sata drive. Since a few days ago, in the morning the system
>>> becomes
>>> really slow due of a really heavy io writing. We investigated and we
>>> think
>>> it might start at night, maybe correlated to to crondaily (standard)
>>> but we
>>> are not sure.  After a few hours the situation returns to normal.
>> Yeah this sounds like something I am quite familiar with...  It's the
>> security check cronjob that runs every day... its looking for any
>> setuid/setgid files, new/modified files...etc... across all file systems
> This is quite likely, so while updating to 10 may not fix the issue
> running on 9.x.

Which means you just told the user to do something that is not likely to
fix the issue but will give them more problems to deal with so they
might forget the original problem in the mean time...  You know this was
the reason I was the Technical Lead for the support teams first in
Europe then in AsiaPAC for Netscape back in the day, and why I never
worked for Microsoft...  You diagnose the problem as best as possible
with as minimal changes to the system at first, then if all else fails
or you come across evidence that points to a known bug that you know is
fixed you tell them to upgrade to the latest *supported* version

> Be aware that 10.3-BETA2 has a known issue related to vnode memory
> usage which can be triggered by such workloads so trying BETA3 when
> released, which should address this would be a good idea.
...supported version... i.e. *NOT* a BETA release - especially if that
beta release has other known issues that might well trigger on the very
problem they indicated...!

Seriously, sorry to pick on you, but "Upgrade to 10.x Beta as it might
help" is not the *first* answer anyone should give... you might as well
have told him to upgrade to 11.... because that has as much chance of
fixing the problem...


Michelle Sullivan

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