Re: How to stress test raid6 on 122 disk array

[Chris Murphy <lists@colorremedies.com>]

On Thu, Aug 4, 2016 at 1:05 PM, Austin S. Hemmelgarn
<ahferroin7@gmail.com> wrote:

>Fedora should be fine (they're good about staying up to
> date), but if possible you should probably use Rawhide instead of a regular
> release, as that will give you quite possibly one of the closest
> distribution kernels to a mainline Linux kernel available, and will make
> sure everything is as up to date as possible.

Yes. It's possible to run on a release version (currently Fedora 23
and Fedora 24) and run a Rawhide kernel. This is what I often do.


> As far as testing, I don't know that there are any scripts for this type of
> thing, you may want to look into dbench, fio, iozone, and similar tools
> though, as well as xfstests (which is more about regression testing, but is
> still worth looking at).
>
> Most of the big known issues with RAID6 in BTRFS at the moment involve
> device failures and array recovery, but most of them aren't well
> characterized and nobody's really sure why they're happening, so if you want
> to look for something specific, figuring out those issues would be a great
> place to start (even if they aren't rare bugs).

Yeah it seems pretty reliable to do normal things with raid56 arrays.
The problem is when they're degraded, weird stuff seems to happen some
of the time. So it might be valid to have several raid56's that are
intentionally running in degraded mode with some tests that will
tolerate that and see when it breaks and why.

There is also in the archives the bug where parity is being computed
wrongly when a data strip is wrong (corrupt), and Btrfs sees this,
reports the mismatch, fixes the mismatch, recomputes parity for some
reason, and the parity is then wrong. It'd be nice to know when else
this can happen, if it's possible parity is recomputed (and wrongly)
on a normal read, or a balance, or if it's really restricted to scrub.

Another test might be raid 1 or raid10 metadata vs raid56 for data.
That'd probably be more performance related, but there might be some
unexpected behaviors that crop up.



-- 
Chris Murphy