[mythtv-users] monthly madam checkarray kills recordings

[scram69]

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"
>
>
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>
> 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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>
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?

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