[mythtv-users] monthly madam checkarray kills recordings

scram69 scram69 at gmail.com
Mon Jan 14 03:32:40 UTC 2019


Wanted to update this thread and find out if anyone else is seeing the same
issue in 18.04.
With speed_limit_max dialed down to 10000 from 100000, recordings from
lower bitrate OTA sources (PBS, ABC) survive, while those from higher
bitrate sources (NBC, CBS) do not.
Of course at that rate, the monthly checkarray literally takes almost half
the month, so I've disabled it in cron.
Has anyone else found a better workaround?

On Wed, May 9, 2018 at 12:45 AM Robin Hill <myth at robinhill.me.uk> wrote:

> 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 :)
> > >>
> > >> _______________________________________________
> > >> mythtv-users mailing list
> > >> mythtv-users at mythtv.org
> > >> http://lists.mythtv.org/mailman/listinfo/mythtv-users
> > >> http://wiki.mythtv.org/Mailing_List_etiquette
> > >> MythTV Forums: https://forum.mythtv.org
> > >>
> > >> 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
> > >
> > >
> > > _______________________________________________
> > > mythtv-users mailing list
> > > mythtv-users at mythtv.org
> > > 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 !!"                 |
>


-- 
________________________
"destroying the fundamental underpinnings of the broadcast television
ecosystem"
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