[mythtv-users] monthly madam checkarray kills recordings

[Robin Hill]

On Tue May 08, 2018 at 08:10:31PM -0700, scram69 wrote:

> On Mon, May 7, 2018 at 8:23 AM, Jay Foster <jayf0ster at roadrunner.com> wrote:
> 
> > On 5/6/2018 4:47 PM, scram69 wrote:
> >
> >
> >
> > On Sun, May 6, 2018 at 4:34 PM, Jerry <mythtv at hambone.e4ward.com> wrote:
> >
> >> On Sun, May 6, 2018 at 7:23 PM scram69 <scram69 at gmail.com> wrote:
> >>
> >>>
> >>>
> >>> On Sun, May 6, 2018 at 2:26 PM, Gary Buhrmaster <
> >>> gary.buhrmaster at gmail.com> wrote:
> >>>
> >>>> On Sun, May 6, 2018 at 4:27 PM, scram69 <scram69 at gmail.com> wrote:
> >>>> > It's the first Sunday of the month, so I've just gone through the
> >>>> first raid
> >>>> > checkarray re-sync on Ubuntu 18.04, having just upgraded from 14.04.
> >>>> > /etc/cron.d/mdadm runs checkarray with the --idle argument,
> >>>> presumably so as
> >>>> > not to kill disk performance for other processes.
> >>>> >
> >>>> > However, during the array check, all recordings failed with
> >>>> > threadedfilewriter errors:
> >>>>
> >>>> "Idle" has different meanings to different apps.
> >>>> You might want to throttle the max i/o rate for
> >>>> sync (a good value will depend on your devices)
> >>>>
> >>>>     dev.raid.speed_limit_max
> >>>>
> >>>> is likely the sysctl to look at.
> >>>>
> >>>
> >>> Thanks Gary.  I still have my old 14.04 system drive mounted.  Before I
> >>> sysctl -w dev.raid.speed_limit_max=some_small_number, do you know where
> >>> I might be able to find what the max speed limit was under Ubuntu 14.04?
> >>>
> >>
> >> cat /proc/sys/dev/raid/speed_limit_max
> >>
> >> should do it :)
> >>
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> >>
> >> Right - that would work if I were actually booted under my old system
> > (AMD64).   Unfortunately, I've upgraded both hardware (kaby lake) and OS,
> > and can no longer boot up with that drive.  With the drive mounted on my
> > new system I can inspect and copy files, but /proc is empty.
> >
> > I sincerely doubt I ever changed that limit under 14.04.  However, I've
> > googled around for quite a while and can't seem to find what the default
> > was.
> >
> > So I guess I'll just try a factor of ten: 200,000 -> 20,000 and see what
> > happens in June...
> >
> >
> > --
> > ________________________
> > "destroying the fundamental underpinnings of the broadcast television
> > ecosystem"
> >
> >
> > _______________________________________________
> > mythtv-users mailing listmythtv-users at mythtv.orghttp://lists.mythtv.org/mailman/listinfo/mythtv-usershttp://wiki.mythtv.org/Mailing_List_etiquette
> > MythTV Forums: https://forum.mythtv.org
> >
> > From my mythbuntu 14.04 system:
> >  cat /proc/sys/dev/raid/speed_limit_max
> > 200000
> > I suspect that 200000 is the default on most linux systems and that there
> > are factors other than that value that are affecting you from the upgrade
> > from 14.04 to 18.04.
> > Jay
> >
> >
> > _______________________________________________
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> > http://lists.mythtv.org/mailman/listinfo/mythtv-users
> > http://wiki.mythtv.org/Mailing_List_etiquette
> > MythTV Forums: https://forum.mythtv.org
> >
> >
> It's very strange: the disk array (raid5, 4 X 3TB) is the one constant from
> the upgrade.  It did not change.  In fact, all I had to do was plug in the
> disks, install mdadm on the 18.04 system, and the array was automatically
> recognized and started.
> 
> So I don't understand why the resync under 18.04 has such a significantly
> different effect on disk performance.  I even diffed the
> /usr/share/mdadm/checkarray script - almost identical between 14.04 and
> 18.04.
> 
> Any idea what might have caused the change?
> 
Probably the kernel version. IIRC, there were changes made to the RAID
code to improve the performance for SSDs, but which lead to higher
impact during rebuilds.

Cheers,
    Robin
-- 
     ___        
    ( ' }     |       Robin Hill        <myth at robinhill.me.uk>  |
   / / )      | Little Jim says ....                            |
  // !!       |      "He fallen in de water !!"                 |