[NCLUG] sw raid, recovery after install

[Stephen Warren]

On 01/16/2013 05:30 PM, Michael Milligan wrote:
> On 01/16/2013 04:36 PM, Stephen Warren wrote:
>> On 01/16/2013 04:07 PM, Michael Milligan wrote:
>>
>>> https://bugs.launchpad.net/ubuntu/+source/mdcfg/+bug/77470
>>
>> Ugggh. I sincerely hope that never gets fixed, or e.g. RAID-1 array
>> scrubbing never has a chance of finding that the mirrors are in sync...
> 
> But who cares

Well, obviously me:-)

If the two drives aren't initially and always exact mirrors of
each-other, the scrubbing process will always say that the arrays
mismatch. That makes the scrubbing process basically useless. Running
the scrubbing process and making sure the two drives don't start to
mismatch is a good RAID monitoring tool. See /usr/share/mdadm/checkarray.

...
> properly at that point.  And a bit later on you aren't sitting there
> twiddling your thumbs waiting for packages to expand on an array that is
> busy copying blocks back and forth between drives slowing down your
> install making it take much longer than it should.  It's painful.  And
> in my case, I have better things to be doing with my time.

At least in recent kernels, the reconstruction is both lower priority
that regular IO, adjustable in min/max performance, and checkpointed so
that if you reboot in the middle, it'll just pick up (roughly I suppose)
where it left off when you next boot up.