Re: performance issue (was: Re: kernel: BUG: soft lockup - CPU#1 stuck for 60s!)

[Neil Brown <neilb@suse.com>]

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Rainer Fügenstein <rfu@oudeis.org> writes:

> Hello Roman,
>
> Saturday, October 24, 2015, 6:31:39 PM, you wrote:
>
>> Use a higher bitmap-chunk size, such as 256M or more.
>
> I guess that would be
>
>    mdadm --grow /dev/md0 --bitmap-chunk=256M    ??

You would need to remove and then re-add the bitmap.  So:

  mdadm --grow /dev/md0 --bitmap=none
  mdadm --grow /dev/md0 --bitmap=intermnal --bitmap-chunk=256M
  
>
> is  it  wise  to issue this command during a re-sync?

Depending on kernel version, it will either work or it won't.
Either way, it won't cause harm.

>
> a  cron.weekly  job started the re-sync (although I'm pretty sure this
> job has been disabled quite some time ago)

Weekly is a bit more often than I would go for, but why disable it?
Regular scanning for latent bad blocks is fairly important for
reliability.

> $ cat /proc/mdstat
> Personalities : [raid6] [raid5] [raid4]
> md0 : active raid5 sdb1[7] sdf1[3] sdc1[5] sde1[0] sdd1[8]
>       11721061376 blocks super 1.2 level 5, 64k chunk, algorithm 2 [5/5] [UUUUU]
>       [==>..................]  resync = 11.9% (348948608/2930265344) finish=7771.1min speed=5533K/sec
>       bitmap: 8/350 pages [32KB], 4096KB chunk

That isn't a cronjob started resync. That would say "check" rather than
'resync".
This looks a lot like a resync after an unclean restart.  But with the
bitmap that should go faster...
What does "mdadm --examine-bitmap /dev/sdb1" report?

NeilBrown


>
> unused devices: <none>
>
> tnx & cu
>
> -- 
> Best regards,
>  Rainer                            mailto:rfu@oudeis.org
>
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